xác định hàm lượng asen trong nước ngầm bằng phương pháp lò graphite (bằng tiếng anh)

Acknowledgment To my supervisor, Assoc. Prof. Dr. Nguyen Van Ri and Master. Nguyen Tien Duc in Department of Analysis Chemistry. I express great appreciation for your time, support patience and guidance throughout this study your continuous enthusiasm and knowledge of the topic relating to this project were an inspiration to me. Also I am thankful to all my classmates for being great friends and helping me so much March, 29 th , 2012 Doan Thi Bich Ngoc 1 Table of Contents Abstract (English) Pollution of arsenic is an acute problem not only in Vietnam but also in worldwide. It is estimated about 57 million people are using surface 2 water with the arsenic concentration is higher than the World Health Organization standard of 10 mg / l (ppb). Arsenic in groundwater is of natural origin and it is released from the sediments due to the anoxic conditions or from the weathered and runoff ores containing arsenic. Arsenic is a poisonous compound that can cause some diseases such as lung cancer, skin cancer, bladder cancer and respiratory diseases. For this reason, there are many studies to find out the useful method to reduce arsenic concentrations in water. In this report, I used the method of atomic absorption spectrometry with graphite furnace to determine the arsenic levels in water and study the use of laterite material to absorb arsenic from water. GF-AAS method is highly sensitive method that can determine the total arsenic in water with high repeatability and detection limits can be achieved ppb levels. Using treated laterite as the adsorbent, water quality is greatly improved, and arsenic can be reduced by 90%, in addition with the low cost and wide applicability. 3 Abstract (Vietnamese) Ô nhiễm asen là một vấn đề vô cùng nhức nhối không chỉ ở Việt Nam mà trên toàn thế giới. Người ta ước tính khoảng 57 triệu người đang sử dụng nguồn nước mặt có hàm lượng asen cao hơn tiêu chuẩn của Tổ chức Y tế Thế giới là 10 μg/l (ppb). Asen trong nước mặt có nguồn gốc tự nhiên và nó được giải phóng ra từ trầm tích do các điều kiện thiếu ôxy hoặc từ các quặng chứa asen bị phong hóa và rửa trôi. Asen là chất độc có thể gây ra một số loại bệnh như: ung thư phổi, ung thư da, ung thư bang quang và các bệnh về hô hấp. Vì lý do đó mà rất nhiều công trình nghiên cứu nhằm tìm ra các phương pháp hữu ích để làm giảm nồng độ asen trong nước. Trong bài báo cáo này, tôi đã sử dụng phương pháp quang phổ hấp thụ nguyên tử với lò graphite để xác định hàm lượng asen trong nước và nghiên cứu sử dụng đá ong để làm vật liệu hấp thụ asen có trong nước. Phương pháp GF-AAS là phương pháp có độ nhạy cao, có thể xác định được tổng hàm lượng asen có trong nước với độ lặp lại cao và giới hạn phát hiện có thể đạt hàm lượng ppb. Sử dụng đá ong có xử lý làm vật liệu hấp phụ, chất lượng nước được cải thiện rất nhiều, hàm lượng asen có thể giảm đến 90%, hơn nữa giá thành rẻ và khả năng ứng dụng rộng rãi. 4 Introduction In history, arsenic in science, medicine and technology has been overshadowed by its notoriety as a poison in homicides. Arsenic is viewed as being synonymous with toxicity. Dangerous arsenic concentrations in natural waters are now a worldwide problem. High arsenic concentrations have been reported recently from the USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan and India. Among them the largest population at risk is in Bangladesh followed by West Bengal in India. Twenty one countries in different parts of the word, groundwater contains arsenic. Many countries in the world are carrying on investigation on arsenic. Historically, colorimetric and gravimetric methods have been used for determination of arsenic. In recent years, atomic absorption spectrometry (AAS) has become the method of choices. However a commonly used technique for the measurement of arsenic is the highly sensitive hydride generation atomic absorption spectrometric method. After examine arsenic, if arsenic is over legal limit in water, those countries must remove arsenic. There are traditionally technologies to remove arsenic from water (oxidation, precipitation/coagulation/membrane separation) with far less attention paid to adsorption. The sorption capacities of both available and developed sorbents used for arsenic remediation together with the traditional remediation methods. We have incorporated most of the valuable available literature on arsenic remediation by adsorption. Existing purification methods for drinking water; wastewater; industrial effluents, and technological solutions for arsenic have been listed. Arsenic sorption by commercially available carbons and other low-cost adsorbents are surveyed and critically reviewed and their option efficiencies are compared. Some commercially available absorbents are also surveyed. An extensive table summarizes the sorption capacities of various adsorbents. Some low-cost adsorbents are superior including treated slag, carbons developed from agricultural waste (char carbons and coconut husk carbons), biosorbents (immobilized biomass, orange juice residue), goethite and some commercial adsorbents, which include resins, gels, silica, treated silica tested for arsenic removal come out to be superior. Desorption 5 of arsenic followed by regeneration of sorbents has been discussed. Strong acids and bases seem to be the best desorbing agents to produce arsenic concentrates. Arsenic concentrate treatment and disposal obtained is briefly addressed. This issue is very important but much less discussed. A: Overview of arsenic Chapter 1: Introducing arsenic 1.1 Properties of arsenic 1.1.1 Identity Elemental arsenic (As) is a member of Group 15 of the periodic table, with nitrogen, phosphorus, antimony and bismuth. It has an atomic number of 33 and an atomic mass of 74.91. Arsenic is ubiquitous and ranks 20th in natural abundance, comprising about 0.00005% of the earth’s crust, 14th in the seawater, and 12th in the human body. It’s concentration in most rocks ranges from 0.5 to 2.5 mg/kg, though higher concentrations are found in finer grained argillaceous sediments and phosphorites. It is a silver-grey brittle crystalline solid, specific gravity 5.73, melting point 817 o C (at 28 atm), boiling point 613 o C and vapor pressure 1mm Hg at 372 o C 1.1.2 Chemical and physical properties of arsenic compounds Arsenic is a metalloid widely distributed in the earth’s crust. It can exist in four valency states; –3, 0, +3, and +5. In strongly reducing environments, elemental arsenic and arsine (–3) can exist. Under moderately reducing conditions, arsenite (+3) may be the dominant form, but arsenate (+5) is generally the stable oxidation state in oxygenated environments. Environmental forms include arsenious acids (H 3 AsO 3 , H 3 AsO 3 , H 3 AsO 3 2- ), arsenic acids (H 3 AsO 4 , H 3 AsO 4 - , H 3 AsO 4 2- ), arsenites, arsenates, methyl arsenic acid, dimethylarsinic acid, arsine, etc. Arsenic (III) is a hard acid and preferentially complexes with oxides and nitrogen. Conversely, arsenic (V) behaves like a soft acid, forming complexes with sulfides. 6 Inorganic forms of arsenic most often exist in water supplies. Arsenic is uniquely sensitive to mobilization (pH 6.5–8.5) and under both oxidizing and reducing conditions among heavy metalloids. Two forms are common in natural waters: arsenite (AsO 3 3- ) and arsenate (AsO 4 3- ), referred to as arsenic (III) and arsenic (V). Pentavalent (+5) or arsenate species are AsO 4 3- , HAsO 4 2 -, H 2 AsO 4 -while trivalent (+3) arsenates include As(OH) 3 , As(OH) 4 - , AsO 2 OH 2 - and AsO 3 3- . 1.2 Arsenic and water Arsenic can be found in seawater (2-4 ppb), and in rivers (0.5-2 ppb). Half of the arsenic present is bound to particles. Freshwater and seas algae contain about 1-250 ppm of arsenic, freshwater hydrophytes contain 2-1450 ppm, marine mollusks contain 1-70 ppm, marine crustaceans 0.5-69 ppm, and fishes 0.2-320 ppm (all values are based on dry mass). In some marine organisms, such as algae and shrimp, arsenic can be found in organic compounds.[1] The legal limit for arsenic in water applied by the World Health Organization (WHO) is 10 µg/L. 1.2.1 Arsenic react with water Elementary arsenic normally does not react with water in absence of air. It does not react with dry air, but when it comes in contact with moist air a layer is formed. The layer has a bronze color, and later develops a black surface. An example of an arsenic compounds that reacts strongly with water is orpiment. This is an amorphous arsenic compound. Reaction mechanism: As 2 S 3 + 6 H 2 O → 2 H 3 AsO 3 + 3 H 2 S In natural water arsenic participates in oxidation and reduction reactions, coagulation and adsorption. Adsorption of arsenic to fine particles in water and precipitation with aluminum or iron hydroxides causes arsenic to enter sediments. 1.2.2 Arsenic present in water Metallic arsenic is processed in lead or copper alloys, to increase hardness. The extremely toxic arsenic gas ASH 3 plays an important role in microchip production. Copper arsenate (Cu 3 (AsO 4 ) 2 .4H 2 O) is applied as a pesticide in viticulture, but its use is currently prohibited in many countries. Paxite (CuAs 2 ) is an insecticide and fungicide. 7 1.3 Effect of arsenic 1.3.1 The environmental effects of arsenic in water Arsenic is an essential compound for many animal species, because it plays a role in protein synthesis. It is unclear whether arsenic is a dietary mineral for humans. Arsenic toxicity is another important characteristic. The boundary concentration of arsenic is 2-46 ppm for freshwater algae. Plants absorb arsenic fairly easily, so that high-ranking concentrations may be present in food. The concentrations of the dangerous inorganic arsenics that are currently present in surface waters enhance the chances of alteration of genetic materials of fish. 1.3.2 The health effects of arsenic in water Arsenic related illness is usually caused by consumption of contaminated drinking water. In the old days it was applied as a poison, because symptoms of arsenic poisoning resemble cholera symptoms, and therefore the intentional factor was shaded. Arsenic in drinking water is an issue of global importance; therefore the legal limit was decreased to 10μg /L. This legal limit is not met in countries such as Vietnam and Bangladesh, where millions of people consume drinking water with an arsenic content of over 50μg /L. This problem results in long- term chronic health effects, such as skin disease, skin cancer, and tumors in lungs, bladder, kidneys and liver. 1.3.3 Arsenic contamination of water in the world Arsenic in natural waters is a worldwide problem. Arsenic pollution has been reported recently in the USA, China, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, New Zealand, Japan, and India. The largest population with known groundwater arsenic contamination is in Bangladesh, followed by West Bengal in India. Larger regions in the USA are affected. Vulnerable areas in Nepal, Pakistan, Thai-land, Laos, Cambodia, and Sumatra have barely or not been examined so far. Many other countries and districts in South East Asia, such as Vietnam, Cambodia, and China have geological environments conducive to generation of high-arsenic groundwater. 8 1.3.3.1 At Bangladesh and West Bengal According to the World Health Organization, “In Bangladesh, West Bengal (India) and some other areas, most drinking-water used to be collected from open dug wells and ponds with little or no arsenic, but with contaminated water transmitting diseases such as diarrhea, dysentery, typhoid, cholera and hepatitis. Programmes to provide ‘safe’ drinking-water over the past 30 years have helped to control these diseases, but in some areas they have had the unexpected side-effect of exposing the population to another health problem—arsenic.” The acceptable level as defined by WHO for maximum concentrations of arsenic in safe drinking water is 0.01 mg/L. The Bangladesh government's standard is at a slightly higher rate, at 0.05 mg/L being considered safe. WHO has defined the areas under threat: Seven of the nineteen districts of West Bengal have been reported to have ground water arsenic concentrations above 0.05 mg/L. The total population in these seven districts is over 34 million, with the number using arsenic-rich water is more than 1 million (above 0.05 mg/L). That number increases to 1.3 million when the concentration is above 0.01 mg/L. According to a British Geological Survey study in 1998 on shallow tube-wells in 61 of the 64 districts in Bangladesh, 46% of the samples were above 0.01 mg/L and 27% were above 0.050 mg/L. When combined with the estimated 1999 population, it was estimated that the number of people exposed to arsenic concentrations above 0.05 mg/L is 28-35 million and the number of those exposed to more than 0.01 mg/L is 46-57 million. [2] 1.3.3.2 United States There are many locations across the United States where the groundwater contains naturally high concentrations of arsenic. Cases of groundwater-caused acute arsenic toxicity, such as those found in Bangladesh, are unknown in the United States where the concern has focused on the role of arsenic as a carcinogen Some locations in the United States, such as Fallon, Nevada, have long been known to have groundwater with relatively high arsenic concentrations (in excess of 0.08 mg/L). Even some surface waters, such as the Verde River in Arizona, sometimes exceed 0.01 mg/L arsenic, especially during low-flow periods when the river flow is dominated by groundwater discharge. [3] 9 1.3.4 Arsenic contamination of water in Vietnam Arsenic contamination of water has become a crucial water quality problem in many part of the world. The contamination of groundwater by arsenic in Bangladesh is the largest poisoning of a population in history. At Vietnam the Vietnamese capital of Hanoi is situated at the upper end of the 11 000 km2 Red River Delta of northern Vietnam, which is inhabited by 11 million people and is one of the most populous areas in the world. Together with the Mekong Delta, the Red River Delta (Bac Bo Plain) has become one of the most productive agricultural regions of Southeast Asia. The rural population is growing rapidly and has, in the last 5-7 yr, moved away from using surface water or water from shallow dug wells as sources for drinking water in favor of groundwater pumped from individual private (family based) tube wells. Groundwater exploitation in the city of Hanoi began 90 yr ago. Today, eight major well fields supply water to city treatment facilities, which process 500 000m3 of water per day. [4-6] The results of the measuring campaign of September 1999 in the rural districts. The results from the investigated family-based tube wells reveal that 50% of the samples exceed the Vietnamese guideline value of 50 µg arsenic per liter with an average concentration of all the samples amounting to 159 µg /l. Peak values of 3000 µg arsenic per liter, south of Hanoi. The situation in a district (peak value of arsenic in water) is particularly alarming: with an average value of 432 µg /l, 90% of the analyzed samples revealed concentrations of 51– 3000 µg /l. 10 [...]... interfacing with computer controlled Wizard software + Being able to switch automatically measuring techniques to measure furnace flame and graphite 5.2 The system is GFA-EX7 graphite + Furnace system, the power supply line, accompanied by accessories: cuvette graphite, graphite electrodes, 5.3 Automatic samplers ASC-6100 + Can be used to increase automation for all measurement techniques: flame, furnace... based on distillation and hydrogen sulfide precipitation methods Beard & Lyerly (1961) reported a gravimetric method for the measurement of arsenic following extraction of arsenic as AsCl 3 by benzene in strong hydrochloric acid The recovery was close to 100% when 20 mg was spiked into an aqueous solution 2.3 Colorimetric methods George et al (1973) carried out a collaborative study for a colorimetric measurement... in operation and maintenance in the local level is absolutely essential for effective use of these plants.[12] 18 B: Experimental Results Chapter 1: Determination of arsenic content in natural water by graphite furnace atomic absorption spectrometry Atomic absorption spectrometry (AAS) is an easy, rapid method and has been widely used for the determination of trace elements in natural water However,... flameless [15] atomic absorption spectrometry Walcerz et al [16] and Sturgeon and Gregoire [17] reported unique preconcentration methods That is, generated hydrides were transferred to the inner wall of the graphite furnace, then the furnace was heated at a high temperature, vaporized As was determined by AAS [18] and ICP-MS [19] However, the hydride generation method has a tendency to interference by coexisting... possibility of selectivity and sensitivity in the detection of a wide range of metals and non-metals including arsenic Popular methods for generating atoms for AAS are flame and electrothermally heated graphite furnaces However, a commonly used technique for the measurement of arsenic is the highly sensitive hydride generation atomic absorption spectrometric method (HGAAS) However, although it is suitable... concentration of elements in the environment to absorb Source emitting a light beam to determine the elements called monochromatic radiation source AAS 6800 + atoms can form chemical flame or no flame (using graphite furnace) has very high sensitivity when to fold hundreds of thousands of times in the flame measurements should be able to identify the elements traces with very small concentrations 7 The parameters... 4.2 Create standard line, limit of dectection (LOD), limit of quatitation ( LOQ) a) Avaluate standard line: To avaluate standard line with full equation based on the results survey of linear range of asen in table 7 and graph 6, we perform create standard line for solution of As with concentration: 2; 5;10;15;20;30;40;50;60;80 ppb Results were caculated by origin 7.5 Graph 7: standard line SUMMARY . các phương pháp hữu ích để làm giảm nồng độ asen trong nước. Trong bài báo cáo này, tôi đã sử dụng phương pháp quang phổ hấp thụ nguyên tử với lò graphite để xác định hàm lượng asen trong nước. hấp thụ asen có trong nước. Phương pháp GF-AAS là phương pháp có độ nhạy cao, có thể xác định được tổng hàm lượng asen có trong nước với độ lặp lại cao và giới hạn phát hiện có thể đạt hàm lượng. (Vietnamese) Ô nhiễm asen là một vấn đề vô cùng nhức nhối không chỉ ở Việt Nam mà trên toàn thế giới. Người ta ước tính khoảng 57 triệu người đang sử dụng nguồn nước mặt có hàm lượng asen cao hơn tiêu