Industrial solid waste recycling in western china

Fenglan Han · Lan’er Wu Industrial Solid Waste Recycling in Western China Industrial Solid Waste Recycling in Western China Fenglan Han Lan’er Wu • Industrial Solid Waste Recycling in Western China 123 Fenglan Han School of Materials Science and Engineering, Circular Economy Technology Institute Beifang University of Nationalities Yinchuan, Ningxia, China Lan’er Wu School of Materials Science and Engineering Beifang University of Nationalities Yinchuan, Ningxia, China ISBN 978-981-13-8085-3 ISBN 978-981-13-8086-0 https://doi.org/10.1007/978-981-13-8086-0 (eBook) © Springer Nature Singapore Pte Ltd 2019 This work is subject to copyright All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or 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Singapore 189721, Singapore Foreword With the implementation of the Strategy on Development of Western China, many leading enterprises in industries such as energy, smelting, and chemicals are concentrated in western part of China and the region has achieved economic boom (GDP of the whole western part of China going up from 2295.5 billion Yuan in 2003 to 12600.3 billion Yuan in 2013) Western part of China takes up more than 60% of energy consumption and 30% of metallurgical and chemical products of the whole country The release of industrial solid waste accounts for over 50% of national total with accumulation of billion tons of industrial solid waste such as fly ash and heavy metal hazardous solid waste In view of environment-friendly and circular use of large amount of industrial solid waste, material research and development task group of Beifang University of Nationalities working with enterprises as well as research institutes and universities such as China Iron and Steel Research Institute, University of Science and Technology Beijing, and Central South University have developed the “production, learning, research, and application” platform Cooperating with Sweden and Australian experts, Beifang University of Nationalities has introduced EU new technologies on environmental protection and recycling and use of industrial waste of smelting industry, and carried out a series of research and development activities It has undertaken and completed several national and provincial research projects on recycling and use of industrial solid waste such as magnesium, manganese, steel, lead and zinc smelting slag, and fly ash Based on relevant findings of this task force, this book collects both Chinese and international research results of this field, and introduces the properties, generation, and pollution characteristics of solid wastes of relevant industries; current status of research and development of environment-friendly technologies as well as some theoretical study results It is expected that the current book could provide precious reference to scientists and engineers in the field of recycling and use of the solid waste In addition, it will also help cultivation and education of high-end talents in relevant field Yinchuan, Ningxia, China October 2017 Academician Jilin He v Preface With rapid economic development in Western China in recent years, there are increasingly urgent needs for treatment, recycling, and reuse of large amount of industrial solid waste It has been noticed that annual generation of industrial solid waste of western part of China takes up about 50% of national total It has become the bottleneck that is affecting sustained development of local economy due to lack of study on environment-friendly and high value-added recycling and use of such solid waste Based on local economic development needs, Beifang University of Nationalities has carried out university–enterprise cooperation on study of industrial solid waste such as magnesium slag, electrolytic manganese residue, fly ash, and so on The current book mainly introduces the research results of Beifang University of Nationalities on recycling and use of industrial solid waste since 2009 The main experimental data and cases come from the findings of the several national research projects such as National Program on Key Basic Research Project of China (973 Program), International S&T Cooperation Project of China, and National Key Technology R&D Program of the Ministry of Science and Technology of China undertaken by the authors This book provides detailed description of the research projects including technical roadmap, experimental data, and industrial test conditions and results, and so on This book involves industrial wastes of magnesium slag, electrolytic manganese residue, lead and zinc smelting acid sludge, fly ash, steel slag and carbide slag, and so on It is expected that the book could provide a reference to scientists and engineers in relevant field and readers with interest There are seven chapters in the book based on different types of industrial solid waste Chapter mainly introduces the classification, properties, hazards, and impacts of industrial solid waste as well as general disposal methods Chapter introduced the generation, property, fluorine, and dust pollution of magnesium smelting slag by Pidgeon process as well as the research on treatment of magnesium slag pollution and reuse of such slag This chapter includes the findings of 973 Program and International S&T Cooperation Project Chapter presents the comprehensive use and treatment of manganese residue This chapter introduces the findings of the cooperation project between the authors and Ningxia Tianyuan Manganese Limited Company, which is the largest electrolytic manganese vii viii Preface enterprise in the world Based on the findings of the research project of National Key Technology R&D Program of the Ministry of Science and Technology of China conducted by the authors with cooperation of Zhuzhou Smelting Group Co., Ltd., Chapter discusses the treatment and disposal of lead and zinc smelting waste acid sludge Chapter presents the circular use of fly ash combining the findings of the China–EU cooperation project Chapter demonstrates the comprehensive use of steel slag Chapter is about the comprehensive use of carbide slag The authors of this book would like to show their thanks to Prof Yuhong Chen, Dr Wanxiu Hai, Dr Hu Zhang, Dr Guiqun Liu, Dr Maohui Li, Dr Zhang Hu Zhang, Dr Maohui Li and Dr Bo Liang for their contributions in the chapters writing The whole book is reviewed and revised by Prof Lan’er Wu Dr Shengwei Guo, Chun Du, and Dr Youjun Lu contributed in reviewing and checking of the manuscript, and Shizhen Zhao has helped on drawing diagrams for the book The authors express their thanks to the financial support of Ministry of Science and Technology of China and Science and Technology Department of Ningxia Autonomous Region Yinchuan, China Prof Fenglan Han Prof Lan’er Wu Contents Introduction 1.1 Solid Waste and Industrial Solid Waste 1.1.1 Solid Waste 1.1.2 Industrial Solid Waste 1.1.3 Difference Between Industrial Solid Waste and Other Solid Waste 1.2 Sources and Classification of Industrial Solid Waste 1.2.1 Sources of Industrial Solid Waste 1.2.2 Classification of Industrial Solid Waste 1.3 Characteristics and Properties of Industrial Solid Waste 1.3.1 Form and Properties of Industrial Solid Waste 1.3.2 Properties of Industrial Solid Waste 1.4 Pollution of Industrial Solid Waste and Its Control 1.4.1 Pollution Characteristics of Industrial Solid Waste 1.4.2 Impacts of Industrial Solid Waste on the Environment 1.4.3 Impacts of Industrial Solid Wastes on Human Health 1.4.4 Controlling Pollution from Solid Waste 1.5 Methods of Treating and Disposing of Industrial Solid Waste 1.5.1 Principle for Treating and Disposing of Industrial Solid Waste 1.5.2 Industrial Solid Waste Treatment Methods 1.5.3 Methods for Disposing Industrial Solid Waste 1.6 Current Status of Use of Industrial Solid Waste References Hazard-Free Treatment and Reuse of Magnesium Slag 2.1 Introduction 2.1.1 Smelting of Magnesium Metal 2.1.2 Generation of Magnesium Slag 2.1.3 Physical and Chemical Properties of Magnesium Slag 1 5 6 26 28 28 30 32 33 34 34 35 36 37 41 43 43 44 50 50 ix x Contents 2.1.4 Major Pollutants in Magnesium Slag 2.1.5 Current Status of Treatment and Disposal of Magnesium Slag 2.2 Efflorescence of Magnesium Slag by Pidgeon Process and Its Prevention 2.2.1 Efflorescence of Magnesium Slag—Phase Analysis of C2 S in Magnesium Slag 2.2.2 Conclusions 2.3 Simulation Study on F Flow in Magnesium Smelting by Pidgeon Process 2.3.1 Development of Pilot Trial Equipment and Pilot Experiment 2.3.2 Simulation of F Migration in Magnesium Smelting Process 2.3.3 Determination of F Content in Magnesium Smelting Process 2.3.4 Change of F Content in the Process of Magnesium Slag Treatment 2.4 Study on F-Free Mineralizer in Pidgeon Magnesium Smelting Process 2.4.1 Study on Borate Mineralizer in Magnesium Smelting by Pidgeon Process 2.4.2 Study on Rare-Earth Mineralizer for Magnesium Smelting by Pidgeon Process 2.4.3 Industrial Test of F-Free Magnesium Smelting Process 2.5 Recycling of Magnesium Slag 2.5.1 Magnesium Slag Replacing Lime as Fluxing Medium for Steel Smelting 2.5.2 Magnesium Slag and Manganese Residue in Preparing of Cement Clinker References Resource Utilization of Electrolytic Manganese Residues 3.1 Introduction 3.2 Properties, Hazards, and Treatment of Electrolytic Manganese Residues 3.2.1 Source of Manganese Residues 3.2.2 Basic Properties of EMR 3.2.3 Environmental Hazards of EMR 3.2.4 Current Status of EMR Treatment 3.3 Technologies Used for Comprehensive Treatment and Recycling of EMR 51 51 53 55 72 73 73 75 78 84 94 95 103 110 112 112 114 123 127 127 131 131 134 137 139 140 Contents xi 3.3.1 Landfill of EMR 3.3.2 EMR Recycling Technologies 3.4 Treatment, Disposal, and Recycling of EMR in Foreign Countries 3.5 Prospect of Comprehensive Treatment and Recycling of EMR References Utilization of Acidic Residue from Lead and Zinc Production Processes 4.1 Introduction 4.1.1 Major Pollutants 4.1.2 Properties and Hazards of Waste Acid Residue 4.1.3 Utilization of Acidic Waste Sludge in China 4.2 Solidification of Heavy Metals in WAR 4.2.1 Heavy Metals in Acidic Waste Sludge Solidified by Magnesium Slag References 140 144 158 159 163 165 165 166 170 178 184 184 203 Comprehensive Utilization of Fly Ash 5.1 Introduction 5.2 Composition and Physicochemical Properties of Fly Ash 5.2.1 Chemical Composition of Fly Ash 5.2.2 Mineral Composition of Fly Ash 5.2.3 Physical Properties of Fly Ash 5.2.4 Composition of Fly Ash Particles 5.2.5 Classification of Fly Ash 5.3 Application of Fly Ash in Building Materials 5.3.1 Application of Fly Ash in Cement Admixture 5.3.2 Application of Fly Ash in Concrete 5.3.3 Application of Fly Ash in Making Foam Glass 5.3.4 Application of Fly Ash in Making Bricks and Building Blocks 5.3.5 Application of Fly Ash in Ceramic Material (Ceramsite) 5.3.6 Application of Fly Ash in Geopolymers 5.4 Application of Fly Ash in Mine Site Backfilling 5.4.1 Basic Description of Mining with Backfilling 5.4.2 Application of Fly Ash in Filling Materials 5.5 Application of Fly Ash in the Treatment of Industrial Effluent 5.5.1 Modification of Fly Ash 5.5.2 Application of Modified Fly Ash for Treatment of Industrial Effluent 5.6 Application of Fly Ash in Flue Gas Desulfurization 207 207 208 208 209 209 212 214 217 217 220 225 229 235 240 244 245 247 256 257 260 264 7.3 The Application of Carbide Slag in Flue Gas Desulfurization Technology 377 CaO + H2 O → Ca(OH)2 (7.3) Ca(OH)2 + SO2 → CaSO3 + H2 O (7.4) CaSO3 + H2 O + SO2 → Ca(HSO3 )2 (7.5) CaSO3 + O2 → CaSO4 (7.6) CaSO4 + 2H2 O → CaSO4 ·2H2 O (7.7) After being de-dusted, the flue gas system lets the flue gas enter the flue gas desulfurization equipment and removes sulfur dioxide after the reaction with the desulfurizer, sending clean flue gas to the chimney, where it is vented into the atmosphere The flow control is performed with the blower fan, while the pressure drop of the flue gas system is overcome through the desulfurizer Additionally, a heat exchanger (GGH) is used to exchange heat The main equipment of the flue gas system include flue, baffle opening, blower fan, and flue gas heat exchanger The flue consists of necessary auxiliary facilities, such as flue and air piping, expansion joint, splite flow plate, and guide plate, flue support, and platform handrail for operation and maintenance In the flue heat exchanger, at the opening of the absorption tower, the clean flue gas is cooled using washing serosity to 45–55 °C, reaching the saturation moisture content In China, the flue gas temperature after GGH, which the flue gas desulfurization equipment requires, is at least 80 °C In the flue gas desulfurization equipment, the absorption system is the most important The main equipment for the absorption system include absorption tower, oxidation blower, circular pump, and demister The core equipment of the flue gas desulfurization system is the absorption tower, which consists of the tower body, the inlet and outlet flue, the access door, the check door, the steel platform handrail, the flange, the liquid level control, the overflow pipe, and other necessary connectors At present, there are four types of absorption towers in China, namely the spray tower, the plate tower, the double circuit tower, and the spray bubbling tower In the design of absorption tower, enlarging the contact area of air and liquid should be considered, which is conducive to converting more sulfur dioxide to calcium sulfite, reduces the loss of pressure and enhances the treatment capacity of flue gas The serosity preparation system is used to dissolve limestone into water, mix it by stirring continuously using a stirrer to avoid sedimentation In the design, the source and quality of limestone are considered If there are significant limestone impurities and it has poor quality, the piping and equipment may be blocked and damaged, which may affect the desulfurization efficiency, reduce the operational life of the equipment, and lead to frequent overhauling of the equipment The gypsum de-watering system is the final process of the desulfurization system The two-stage dehydration pattern of hydrocyclone dehydration in combination with vacuum belt dehydration is used The “gypsum serosity” having the concentration of 20–30% after the desulfurization reaction is sent to hydrocyclone using seros- 378 Comprehensive Utilization of Carbide Slag ity discharging pump for the first-stage dehydration The “gypsum serosity” with the concentration of around 50% enters the vacuum belt filter separator for further separation of moisture, where the moisture content is further dried out to meet the requirement of the gypsum with water content of 10–15% The main factors affecting the desulfurization using limestone (lime)–gypsum wet method are as follows (1) Velocity of flue gas: when other parameters are fixed, the desulfurization tower will increase the velocity to speed up the mutual kinematic velocity of gas and liquid, resulting in the formation of a thin film between the gas and liquid phases The serosity is relatively thin and increases the contact surface between the gas and liquid Meanwhile, the speed at which the serosity is sprayed from the spray thrower is relatively reduced, leading to an increase in the quantity of serosity per unit volume The reaction of sulfur dioxide (SO2 ) and serosity is relatively sufficient, enhancing the running efficiency of desulfurization equipment However, the enlargement of the velocity of flue gas may cause an overflow of serosity Since the flue gas takes a large amount of moisture, this increases the load on demister, due to which, the equipment must be enlarged The determination of velocity of flue gas should consider the type of desulfurization tower according to the test and operating conditions If the desulfurization tower uses a spray tower, the velocity of flue gas is usually controlled within the range of 3–5 m s−1 (2) Liquid-to-gas ratio (L/G): the liquid and gas ratio is the ratio between the amount of gas at the opening of desulfurization tower and the corresponding amount of sprayed serosity The value of L/G ratio affects the desulfurization efficiency As in the design of desulfurization tower, the SO2 absorber’s superficial area is decided by the amount of circulating serosity When all other parameters are kept constant, the desulfurization tower can increase the L/G ratio to enhance the desulfurization efficiency Many researchers have built different mathematic models for desulfurization, including the mathematic model of Hu et al [26] (3) Flue gas humidity: the flue gas inside the desulfurization unit should eliminate humidity because, more humid the flue gas, higher is the absorption rate of SO2 and easier it is for HSO3 − to form However, the low temperature of flue gas may reduce the reaction rate of SO2 and desulfurizer (4) pH value of serosity: the pH value of serosity is one of the important parameters for limestone method The enhancement of pH value of serosity may reduce the mass transfer resistance of the liquid phase and speed up the rate of absorption of SO2 In addition, the decrease in pH value of serosity can promote the dissolution of limestone, whereas CaSO3 can be easily oxidized into CaSO4 However, a too low pH value of serosity may corrode the equipment and piping, enhance the requirement for equipment material, and increase the equipment cost Therefore, it is very important to select a reasonable pH value for flue gas desulfurization system, which is usually controlled within the range of 5.5–6.0 7.3 The Application of Carbide Slag in Flue Gas Desulfurization Technology 379 (5) Inlet SO2 concentration: when all other parameters are kept constant, if SO2 concentration is increased and the alkalinity of serosity is not enhanced, the desulfurization efficiency of the desulfurization tower will be reduced (6) Duration of the residence time of slurry: the duration of stay of serosity in the flue gas desulfurization system is usually controlled to within 12–24 h and at this time, the reaction between sulfur dioxide and serosity is sufficient Meanwhile, there is enough time to oxidize CaSO3 into CaSO4 Long time of stay may enlarge the volume of serosity pool, which increases the corresponding equipment size, thus leading to an increase in investment However, if the time of stay is too short, the reaction time between sulfur dioxide and serosity is insufficient and the desulfurization efficiency is not high enough (7) Absorbent: higher the effective constituent of absorbent, more is the desulfurization efficiency However, higher the quality of limestone, higher is the purchase cost It is generally required that the granularity of limestone absorbent be within 200–300 mesh, while the purity be approximately 90% (8) Degree of supersaturation of absorbent: the supersaturation of absorbent in flue gas desulfurization system is controlled within 110–130% to maintain the absorption liquid within the range of saturation degree This will not cause scaling on the surface of equipment, which usually leads to the blockage of equipment (9) Ash content in flue gas: when the ash content in flue gas is higher, the contact surface between SO2 and desulfurizer will be affected and the absorption surface of SO2 will be reduced, which leads to the decrease of chemical reaction rate In addition, as the flying ash contains some heavy metal ions, the reaction rate of Ca2+ and HSO3 − will be decreased, due to which the desulfurization efficiency will be reduced The operation rate of the flue gas desulfurization system using limestone method reaches more than 99% and the running is reliable The control of all the indicators can enhance the desulfurization efficiency to 95% For example, the × 360 MW generator set of Luo Huang of Chongqing (China) uses the desulfurization technology using limestone–gypsum method Its treatment capacity of flue gas reaches 100%, while the desulfurization indicators meet the requirement for environmental protection Furthermore, the desulfurization rate in the actual production exceeds 95%, whereas the purity of gypsum is larger than 90% Additionally, the production reaches the value of 330,000 tons [27] The price of limestone is higher and accounts for 30% of the running cost of desulfurization equipment In order to enhance the running economic benefits of the power plant and reduce the running costs, the matching power plant of PVC producing enterprises uses carbide slag to substitute the desulfurizer Due to this reason, the production costs are effectively reduced 380 Comprehensive Utilization of Carbide Slag Flue gas desulfurization technology using carbide slag–gypsum wet method (1) Desulfurization principle of carbide slag SO2 in flue gas is dissolved in the absorption liquid, which changes from gaseous state to liquid state and then is dissociated into H+ and HSO3 − according to Reaction Equations (7.8)–(7.10) [28] SO2 (g) SO2 (aq) SO2 (aq) + H2 O H2 SO3 (aq) H2 SO3 (aq) + H2 O H+ + HSO− (7.8) (7.9) (7.10) The Reaction Equation (7.8) shows that SO2 is changed from gaseous state to liquid state, while the reaction speed is slow, which is one of the main factors affecting the absorption reaction rate The Reaction Equation (7.10) occurs mainly in the upper part of the absorption tower’s serosity tank or when the spraying liquid falls, and the inlet air forcefully oxidizes it to cause the dissolution of HSO3 − to SO4 2− and H+ according to Reaction Equation (7.11) HSO− + O2 (g) + SO2− +H (7.11) In the upper part of the serosity tank, the buffering serosity system consists of SO4 2− and HSO3 − The reaction equation of the ionization of the main ingredient Ca(OH)2 of carbide slag in water is given by Reaction Equation (7.12) Ca(OH)2 (s) Ca2+ + 2OH− (7.12) The dissociation reaction speed of Ca(OH)2 in water solution is fast, and the resulting Ca2+ and SO4 2− undergo a chemical reaction, producing gypsum, which is dried afterwards (see Reaction Equation (7.13)) Ca2+ + SO2− + 2H2 O CaSO4 ·2H2 O ↓ (7.13) The flue gas after being de-dusted enters through the pipe from the bottom of desulfurization tower and moves upward It flows downward with the absorbing serosity sprayed from the spraying nozzle, resulting in full countercurrent contact between the gas and liquid phases in the absorption tower This leads to mass transfer, which results in the dissolution of sulfur dioxide and sulfur trioxide in the serosity, generating sulfurous acid and vitriol according to Reaction Equations (7.14)–(7.15) SO2 + H2 O H2 SO3 (7.14) 7.3 The Application of Carbide Slag in Flue Gas Desulfurization Technology SO3 + H2 O H2 SO4 381 (7.15) As in the flue gas, there are some acid compounds, such as HF and HCl, which are dissolved in serosity during spraying to form hydrofluoric acid and hydrochloric acid When the pH value is low, sulfurous acid is dissociated into H+ and HSO3 − , and when pH value is high, HSO3 − is dissociated into H+ and HSO3 − These reactions are represented by Reaction Equations (7.16)–(7.17) H2 SO3 + HSO− + H (lower pH) (7.16) HSO− + SO2− + H (higher pH) (7.17) The corresponding dissociation of H2 SO4 and a small amount of HCl and HF occurs in the absorption liquid, which generates a large amount of H+ during dissociation, leading to the decrease of pH value of the serosity In order to enhance the ability of serosity to absorb SO2 continuously, the H+ ions generated in the dissociation reaction need to be removed The method to remove H+ consists of the addition of desulfurizer carbide slag in the serosity H+ ions produce a neutral reaction with OH− in the carbide slag serosity In this way, the generated H+ are removed and the ability to absorb SO2 is enhanced Furthermore, hydroxide ions enter the absorption tower and produce a neutral reaction as given by Reaction Equation (7.18) 2+ Ca2+ + 2OH− + HSO− + SO2− → Ca + 2H2 O (7.18) Under acidic conditions, the SO3 2− ions generated in the reaction may react according to Reaction Equation (7.19) + SO2− +H HSO− (7.19) After absorbing SO2 , the serosity contains a large amount of SO3 2− and HSO3 − , which are strong reducing agents and can be oxidized by oxygen in the serosity (see Reaction Equations (7.20) and (7.21)): 2− SO2− + O2 → SO4 2− + HSO− + O2 → SO4 + H (7.20) (7.21) Furthermore, oxygen is continuously flown into the reaction pool through oxidation air system due to which SO3 2− and HSO3 − are oxidized continuously into SO4 2− 382 Comprehensive Utilization of Carbide Slag At the pH value of the flue gas desulfurization technique using carbide slag— gypsum wet method, OH− dissociate from Ca(OH)2 producing a neutral reaction with H+ , which are dissociated from sulfurous acid This way, a large amount of Ca2+ , SO3 2− , and SO4 2− are left in the serosity When certain concentration values are reached, the hardly solvable compound generated by the three ions will be precipitated out from the solution according to Reaction Equations (7.22) and (7.23) 1 Ca2+ + SO2− + H2 O → CaSO3 · H2 O 2 (7.22) Ca2+ + SO2− + 2H2 O → CaSO4 ·2H2 O (7.23) The overreaction is given by Reaction Equations (7.24) and (7.25) Ca(OH)2 + SO2 + O2 + H2 O → CaSO4 ·2H2 O 1 Ca(OH)2 + SO2 → CaSO3 · H2 O + H2 O 2 (7.24) (7.25) Due to forced oxidation, that is, due to the continuous flow of oxygen into the reaction pool using oxidation air system, the SO2 absorbed by the serosity will be almost completely oxidized to generate calcium sulfate dihydrate (CaSO4 ·2H2 O) (gypsum) The control of indicator of the degree of supersaturation of the desulfurization equipment’s liquid phase (calcium sulfate dihydrate (CaSO4 ·2H2 O)) can not only prevent its scaling but also produces gypsum of high quality After the sulfur dioxide in flue gas is washed by the carbide slag absorbent, the clean flue gas removes the fog drops through a demister, and then, it is discharged into the atmosphere through the chimney (2) Comparison of the dissociation mechanism between carbide slag and limestone The dissociation mechanism of carbide slag from SO2 is completely different from that of the limestone However, the corresponding mechanism of Ca(OH)2 is much different from that of the limestone First, the solubility and rate of dissolution of Ca(OH)2 in water are higher than those of limestone The solubility of Ca(OH)2 in water is 1.608 kg m−3 , which is approximately 10,000 times that of the limestone in water Many researchers think that the main factors affecting the dissolution of limestone are the pH value and grain size [29] Second, no CO2 is generated in the process of desulfurization of carbide slag The reaction balance is not affected by the escape velocity of CO2 Furthermore, the rate of absorption reaction is large, while the corresponding reaction time is short Meanwhile, OH− dissociated by carbide slag produce a neutral reaction with H+ dissociated by Ca(OH)2 and generate H2 O, thus driving the chemical reaction to proceed in the forward direction This in turn increases the desulfurization efficiency (see Fig 7.5 [28]) 7.3 The Application of Carbide Slag in Flue Gas Desulfurization Technology 383 Fig 7.5 Dissolution of carbide slag and limestone (Reprinted from Ref [28], Copyright 2011, with permission from Huadian Technology) (3) Comparison of techniques of carbide slag method and limestone method Both the techniques of carbide slag method and limestone method use Ca element Their processes are basically the same The main difference is that of the combined state of Ca Ca in the carbide slag method exists mainly in the form of Ca(OH)2 and that in the limestone method exists in the form of CaCO3 Compared to CaCO3 , the reactivity of Ca(OH)2 is higher Meanwhile, Ca(OH)2 is slightly soluble in water, whereas CaCO3 is less soluble in water than Ca(OH)2 This way, Ca2+ concentration in Ca(OH)2 solution is higher than that in CaCO3 solution Among the carbide slag desulfurization methods, in the spray reaction section of the desulfurization tower, the reaction speed of sulfur dioxide and calcium hydroxide is much higher than that of the limestone method Therefore, under the condition that the flue gas volume and the sulfur content at the opening of the desulfurization tower are the same, the L/G ratio of carbide slag method is relatively small, which means that, when carbide slag is used as a desulfurizer, the circulating amount of serosity is small and the running cost is less Meanwhile, the use of a large amount of carbide slag in desulfurization not only reduces the discharge of solid waste (carbide slag), but it also decreases the environmental pollution and achieves better environmental benefits In addition, the use of slag reduces the cost of desulfurizer and decreases the mining of already limited resource of limestone Furthermore, the carbide slag method can reduce a large amount of CO2 generated in the ordinary limestone— gypsum method, thus achieving economic, environmental, and social benefits The desulfurization efficiency of carbide slag method for medium and low sulfur coal is more than 98% However, as no CO2 is generated in the process of carbide slag desulfurization, the balance of reaction is not affected by the escape velocity of CO2 Furthermore, the speed of absorption reaction is fast, whereas the absorption reaction may cause fluctuations in pH value Therefore, the running stability of the desulfurization system using carbide slag method is lower than that of the limestone method In the actual 384 Comprehensive Utilization of Carbide Slag production, the pH value in the serosity pool of desulfurization tower is usually controlled within the range of 6–8 Scaling will easily occur when using carbide slag desulfurization, which would result in blocking of pipe, equipment, and nozzles In order to prevent scaling, the degree of supersaturation of liquid phase calcium sulfate dihydrate (CaSO4 ·2H2 O) in the desulfurization equipment, while the concentration of entering carbide slag must be controlled In the actual production, the solid content of carbide slag serosity into the tower is usually controlled at around 15% (4) Progress of research on desulfurization using carbide slag method Tong Yan and others used SO2 in the hydrochloric acid simulated flue gas to conduct research in the tank reactor on the effect of reaction temperature and pH value on the dissolution of carbide slag [30] Although the examples of desulfurization using carbide slag were reported in previous studies, many problems appeared in the running process For example, the ingredient of carbide slag was more complex, while the quality was hard to be ensured The viscosity of serosity was strong, which easily led to blocking of piping, wear, and corrosion of the system The desulfurization buffering of carbide slag serosity was poor, which was not advantageous to the stable running of the system [31–34] Xu Jianhong and others used bubble absorption equipment and comprehensively compared the buffering capacity of pH value and desulfurization efficiency during the process of desulfurization using carbide slag and limestone They conducted research on the effect of three organic acids, used as additives, to strengthen the desulfurization performance of carbide slag [35] Zhejiang Ju Hua Group (China) converted carbide slag into dry powder and used the NID technique for the desulfurization process The desulfurization efficiency for the flue gas of thermal power plant reached more than 90% Carbide slag can also be used as sulfur-fixing agent for industrial coal-fired boilers When mixed evenly in a certain proportion, SO2 discharged during coal’s combustion reacts with carbide slag to generate CaSO3 and CaSO4 , thus fixing the sulfur 7.4 Application of Carbide Slag in Other Fields 7.4.1 Carbide Slag as a Building Material The main constituent of carbide slag is Ca(OH)2 , which can be used as raw material for producing building material Shandong Cement Products Factory (China) succeeded in developing the technology of using carbide slag to produce light cinder brick Its product quality is similar to that of the same variety of product, which does not contain carbide slag This brick uses concentrated carbide slag (water content is 39.6%) as the main raw material A small quantity of cement is added, and the system is stirred evenly with coal cinder (grain size is less than 20 mm) The road metal is smashed in the proportion 7.4 Application of Carbide Slag in Other Fields 385 of carbide slag:cement:road metal:coal cinder = 3.2:1.1:3.2:2.5, respectively, and a block machine is used for pressure forming The product is maintained naturally for appropriately 28 days The strength of light calcium carbide–coal cinder brick approaches that of the ordinary red brick, conforming to the national standard on small-sized hollow blocks However, the advantage is that the investment is low, whereas the cost is also less The weight of the product is light, while it can be produced and maintained under normal temperature and pressure This way, energy is saved, and its cost is 60% of that of the ordinary brick, and 50% of that of the concrete block The light brick produced using carbide slag is widely used, which not only comprehensively utilizes carbide slag, enhances the economic benefit, and turns “waste” into wealth but also protects the environment, which is an added benefit to this product However, in the production process of light cinder brick, calcium carbide waste residue is added as the calcareous material Its addition is limited, usually not exceeding 15–35% For an enterprise with a high discharge of slag, it is hardly completely digestible In addition, the marketing of cinder brick is not smooth, which restricts the development of product Carbide slag–coal cinder or carbide slag–coal ash can be used to produce building bricks The steam-pressing brick, which Gao Wenyuan developed, used carbide slag and coal ash as the raw materials and had the rupture strength of more than MPa [36] Apart from producing building materials, carbide slag can also be used as roadbed material Coal ash–carbide slag is completely qualified as a roadbed material It has characteristics, such as short construction time limit and high efficiency Furthermore, it can reduce cost and decrease the harm of waste residue to environment 7.4.2 Carbide Slag in the Production of Ordinary Chemical Products Producing products, such as calcium oxide, bleaching powder, and calcium carbonate Carbide slag is used to substitute limestone to produce many chemical products, which require Ca(OH)2 These products include calcium oxide, bleaching powder, and calcium carbonate Carbide slag is dehydrated, dried, and burnt at 800–900 °C to prepare high-activity calcium oxide, which can be used in fields, of building material After pretreating carbide slag, NaOH is added in a certain proportion The mixture is dissolved in water and chlorine is introduced to prepare bleaching powder Producing epoxypropane Epoxypropane is an important chemical raw material and a large amount of slaked limes are needed to produce epoxypropane using chlorohydrin process, which uses propylene, oxygen, and slaked lime as raw materials 386 Comprehensive Utilization of Carbide Slag Fujian Province Southeast Electrochemical Company (China) is a large enterprise, which produces PVC (70,000 t/a) using acetylene method At present, carbide slag is used to substitutes slaked lime to produce epoxypropane in Meizhou Bay Chlor-alkali Industrial Company, China Its chemical reaction process is as follows: propylene, chlorine, and water react in a tubular reactor, whereas the tower reactor is used to generate chloropropanol, which is mixed with treated carbide slag The mixture is sent to saponified tower of epoxypropane, where a saponification is produced using Ca(OH)2 (carbide slag) to generate epoxypropane As the quality fraction of Ca(OH)2 in carbide slag is as high as more than 90%, while the average quality fraction of Ca(OH)2 in domestic slaked lime is only 65%, the use of carbide slag not only decreases the production cost of epoxypropane by around 130 yuan/t but also decreases the handling capacity of solid impurities, which not take part in the reaction and are less than those using slaked lime The use of carbide slag to produce epoxypropane can not only fully utilize carbide slag, turn wastes into wealth but also ensure that the quality of produced epoxypropane is stable and conforms to national standards Producing potassium chlorate Process of using carbide slag to substitute lime to produce potassium chlorate is as follows First, the impurities present in carbide slag serosity are removed, after which it is placed in the setting pool to obtain emulsion with the concentration of 12% The emulsion is pumped to chlorination tower, and chlorine and oxygen are added to it In the chlorination tower, Ca(OH)2 produces the saponification with Cl2 and O2 to generate Ca(ClO3 )2 After removing free chlorine, the plate-and-frame filter press is used to remove solid substance and produce a double decomposition reaction of the obtained solution and KC1 to generate KClO3 solution This step is followed by evaporation, crystallization, dehydration, drying, smashing, and packing in order to prepare the product potassium chlorate (KClO3 ) The overall reaction is given by Reaction Equations (7.26) and (7.27) Ca(OH)2 + Cl2 + O2 → Ca(ClO3 )2 + H2 O (7.26) Ca(ClO3 )2 + KCl → KClO3 + CaCl2 (7.27) The production of t potassium chlorate uses 10 t of carbide slag and saves t lime, and 420 yuan of raw material cost It is technically feasible to use carbide slag to substitute lime for producing potassium chlorate (KClO3 ) The purpose of comprehensive utilization of carbide slag can be realized, which not only reduces the harm to environment but also reduces the pollution caused by the transportation of lime and improves the working conditions The use of carbide slag as a building material and a roadbed material is an effective way of largely treating carbide slag, which can not only save cost but can also reduce waste However, for the manufacturers generating carbide slag, although the problem of treating wastes has been solved, there is still no economic benefit The use of carbide slag in the field of environmental protection can realize the purpose 7.4 Application of Carbide Slag in Other Fields 387 of treating wastes However, the quantity is limited Since the carbide slag is used to make ordinary chemical products, its preprocessing procedure is complex, and the product price is not high Due to these reasons, the economic benefit is limited and the manufacturer lacks enthusiasm to use and process it This is why, manufacturers normally discard carbide slag, which not only leads to waste of resource but also pollutes the environment Therefore, it is of significance to find a new carbide slag resource utilization way to turn it into a product with high added value and improve manufacturers’ motivation 7.4.3 Carbide Slag for Preparing Nanocalcium Carbonate The preparation of carbide slag for preparing nanocalcium carbonate is one of the better ways to use it Nanocalcium carbonate is a novel solid material, characterized by nanocrystallization, high whiteness, large loading capacity, and strengthening effect It is widely used in fields, such as rubber, plastics, and papermaking Domestically, the market potential of nanocalcium carbonate is huge The market price is much different because of the different performances and applications The price lies within the range of 2000–12,000 yuan per ton At present, the domestic manufacturers of nanocalcium carbonate obtain raw materials by exploiting limestone, which is disadvantageous to environmental protection If the discarded carbide slag can be used to prepare nanocalcium carbonate not only the harm of carbide slag to environment can be eliminated but the economic benefits can also be obtained At present, only Wu et al have developed a technique for using carbide slag to prepare nanocalcium carbonate [37] During the preparation process, carbide slag is purified first Then, it is calcined at 800–900 °C to obtain CaO, after which CaO is slaked and converted to Ca(OH)2 solution with the quality fraction of 4–10% Then, the additives are added, and CO2 is carbonized with the volumetric concentration of 15–30% The carbonization temperature is controlled within the temperature range of 20–30 °C After a series of treatment steps, nanoscale activated chalk is obtained Its grain size is 30–50 nm However, this technique is still too complex since it must be washed and requires high-temperature calcination for pretreating carbide slag Therefore, its energy consumption is high, and the secondary pollution may easily occur It needs sand grinding after the carbonization process, which also takes a long time Therefore, it is very urgent to find a simple, high efficiency, and low-cost new technique to prepare nanocalcium carbonate The preparation of nanocalcium carbonate using carbide slag mainly includes three steps of pretreatment, carbonization, and surface modification Carbide slag contains many impurities, which should be effectively removed in the pretreatment step These impurities may affect the steps of carbonization and surface modification and even affect the performance of final nanocalcium carbonate After resolving the challenges of pretreatment, the existing method can be used for carbonization and surface modification to prepare nanocalcium carbonate in order to meet the need and to realize the purpose of turning carbide slag into wealth 388 Comprehensive Utilization of Carbide Slag 7.4.4 Carbide Slag for Producing Unslaked Lime for Calcium Carbide Louisville City Air Reduction Plant of Kentucky (United States) realized the urgency of treating carbide slag serosity In 1948, it built an unslaked lime test device with the daily production of 60 t, while in 1959 and 1962, it built two sets of 330 t/a unslaked lime production devices, which run safely and reliably They run for nearly 350 days per year The technique of producing lime with calcium carbide is as follows Carbide slag is dried and its solid content is adjusted to around 60% It is conveyed and distributed evenly to the pelletizer at ¾ of the length of the pelletizer Then, it is granulated and converted into balls of 5–20 mm These balls are dried through the pneumatic drying furnace (350 °C) and calcined in the rotary furnace (900–1000 °C) The drying of material in the drying furnace is conducted using the hot waste gas from the rotary furnace The calcined reburned lime flows into the discharge hopper and is loaded and transported to the calcium carbide plant to be used as calcium carbide raw material Specifications of lime products CaO is no less than 86%, whereas CO2 is no less than 1.0% The moisture content is 0.5%, whereas the impurity (Fe2 O3 , H2 SiO3 ) is not more than 13% Finally, the granularity is 5–20 mm Raw material and power consumption as follow: (calculated for producing t of lime) Carbide slag 1.33 t; water m3 ; electricity 37 kWh; steam 0.16 t; coal ash 0.111 t; nitrogen m3 ; fuel gas 388 m3 ; fuel oil 0.001 t This method is technically feasible and is the better treatment method for producing lime This is due to certain reason First, the investment on the production of lime is less than 1/10 of that on cement Second, lime is the raw material for producing calcium carbide There is no question of finding another market Calcium is used as a carrier to realize a closed cycle of carbide slag–lime–calcium carbide–carbide slag Third, the factor of restricting itself should be reduced The PVC using calcium carbide method can further enhance the scale of production Meanwhile, the limestone resources are protected The economic benefits are obtained, and the social benefit comes along with the novel production of lime using carbide slag technique, which cannot be obtained using other treatment methods However, this method consumes high energy Carbide slag can be reused as calcium carbide raw material For example, it can be added in 20% of calcium carbide to be used as raw material The amount should not be too much since the reburned lime contains sulfur and phosphorus impurities, which may affect the quality of calcium carbide 7.4 Application of Carbide Slag in Other Fields 389 7.4.5 Other Treatment Methods of Carbide Slag Carbide slag is used for industrial wastewater treatment, which can reduce cost and realize the treatment of wastes Carbide slag can be used to neutralize acidic wastewater and electroplating wastewater The carbide slag with certain water content and percolate have strong basicity They also contain harmful substances, such as sulfide and phosphide In accordance with the “Identification Standards for Hazardous Wastes” (GB5085-2007), carbide slag belongs to Class II of General Industrial Solid Wastes, which cannot be discharged directly into seawalls or valley Additionally, if it is used for land reclamation and ditch filling, the anti-seepage measures must be taken in accordance with the “Regulations on the Design of Landfill Sites of Industrial Chemical Waste Residue” (HG20504-92) Stacking by Land reclamation and ditch filling Some plants built close to the coast or in mountain areas have discharged carbide slag directly into seawalls or valleys Some of them have stacked by land reclamation and ditch filling However, there is almost no anti-seepage treatment This method occupies a large area and the pollution is serious Selling after natural setting Most plants use the natural setting method They discharge carbide slag into a setting pool or low-laying area After the slag is evaporated naturally and precipitated, it is excavated manually or using a forklift or grabbed using buckets for selling Similarly, there is no anti-seepage treatment for the storage area The treatment effect using the natural setting method is unstable It is affected by the environment and the meteorological conditions Especially, large amounts of rainfall and small amount of evaporation capacity prevail in the south In rainy seasons, the water content of precipitate is high and is usually around 50–60%, showing as a thick pulpous state They cannot be excavated and utilized at all References Yao EL, Wang XQ (2013) Development and tendency predict of comprehensive utilization of carbide slag of chlor-alkali industry Chin Chlor-Alkali (2): 40–42 Tao L, Zhang ZH (2016) Current situation and development trend of PVC industry in China Polyvinyl Chloride 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carbide slag N Wall Mater Constr (8): 35–36 37 Wu QW, Shi LY, Zhang ZY (2002) Preparation of nanometer calcium carbonate particles by calcium carbide residue J Shanghai Univ (Nat Sci Ed) 8(3): 247–250 .. .Industrial Solid Waste Recycling in Western China Fenglan Han Lan’er Wu • Industrial Solid Waste Recycling in Western China 123 Fenglan Han School of Materials Science and Engineering, Circular... so-called solid waste, in fact, includes solid and semisolid waste, liquid waste excluding liquid waste discharged into waters, and gaseous waste in containers 1.1.2 Industrial Solid Waste The definition... prescribed industrial solid wastes can be treated by marine disposal and landfilling Finally, the current status of industrial solid waste used is investigated Keywords Industrial solid waste · Waste