17:15 〜 18:45
[AGE29-P04] Evaluation of pH-dependent on arsenic adsorption and desorption process of laterite
キーワード：ヒ素、熱処理ラテライト、ｐH、吸脱着、バッチ試験、ラングミュア等温曲線
Arsenic is toxic and carcinogenic and Long-term consumption of water containing arsenic can cause serious health problems, including cancer and cardiovascular disease. Arsenic in groundwater affects around 108 countries and endangers more than 230 million people. Existing arsenic removal technologies have drawbacks in terms of removal capacity and cost. Laterite is a soil rich in aluminum and iron hydroxides and is said to cover 1/3 of the world's land surface. The laterite has a positive surface charge, facilitating anionic metal adsorption in surface area. Adsorption of arsenic is related to the -OH group. Adsorption and desorption of arsenic may be controlled by changing the pH of the arsenic solution. Thermal treatment of laterite has been found to increase its adsorption capacity. In this study, the sample was prepared thermal-treated by heating at 500°C for one hour. Oxidation of hydroxyl groups on laterite surface to acid groups by thermal treatment. This increases adsorption capacity by 2 to 10 times that of raw laterite. This study aimed to establish the arsenic desorption process of laterite for reuse and verify how the amount of adsorption and desorption changes with changes in pH. Raw laterite (RL) and thermal treatment laterite (TTL) from Vietnam were used. I prepare 3types of grain sizes (0.25-0.60mm, 0.60-2.00mm, 2.00-4.75mm). Batch tests were performed using these. The adsorption test procedure is described below. Place 30mL of arsenic solution and 3g of RL or TTL as adsorbent in the same bottle (liquid-solid ratio 10). Shake the bottle at 20°C for 24 hours at 100 rpm. After shaking, centrifuge at 8000 rpm for 15 minutes and filter through a 0.22 µm membrane filter to make a test solution. Analyze the test solution with an atomic absorption spectrophotometer to determine the concentrations of arsenic, iron, aluminum, and calcium. Before and after the adsorption test pH, and EC are measured with a portable meter. The following is a description of the desorption test procedure. Place 30 mL of deionized water and 3 g of used adsorbent in the same bottle (liquid-solid ratio 10). The pH of the deionized water is varied depending on the test. Adsorption and desorption rates are calculated from arsenic's initial, after-adsorption, and after-desorption concentrations. In the first preliminary test, a solution with an initial concentration of arsenic of 100 mg/L and pH 2 was prepared for the adsorption test. RL and TTL with particle sizes of 0.25-0.60 mm were used as adsorbents. Deionized water adjusted to pH 2 was used in the desorption test. Preliminary test results showed that the adsorption rate by RL was 96.8% and that by TTL was 98.4%. The desorption rate from RL was 1.61% and from TTL was 3.02%. Under the preliminary test conditions, desorption was found to be unlikely to occur for both RL and TTL. It is necessary to find the conditions under which further desorption occurs. Further tests are needed to find the conditions under which further desorption occurs. Specific examples, (1) Repeat the adsorption and desorption tests alternately. (2) Repeat only the desorption test several times after adsorption and desorption. (3) Change the pH of the solutions and deionized water used in the adsorption and desorption tests to 4, 6, and 8. Previous studies have shown that an increase in OH- in solution competitively reacts with soluble hydroxyl complexes and decreases the adsorption of arsenic on laterite. Therefore, in experiment (3), the desorption rate is expected to increase at pH 8. The tests will also be carried out using solutions with initial arsenic concentrations of 50, 250, 500, 750, and 1000 mg/L to generate isothermal adsorption and desorption curves. The Langmuir equation is used to generate the isothermal curves.