COMPOSITE GEOLOGICAL MATERIALS FOR TREATMENT OF ARSENIC IN GROUNDWATER

Abstract

Arsenic contamination in groundwater is an important problem in many countries and responsible for many life-threatening diseases such as black fever, cancer, neurological and cardiovascular diseases, and diabetes. Despite the proposal of several remediation techniques worldwide, it has been challenging to find a cost-effective method to remove arsenic from groundwater in Thailand. This research is thus aimed to study chemical and physical properties of geological materials to create cost-effective adsorbents for arsenic removal. The most effective adsorbent is made of porous siltstone, expanded perlite, and soil sample at the ratio of 66.67 to 16.67 to 16.67, respectively. The adsorbents are tested with arsenic contaminated water at different conditions and suggest that the most suitable condition is to use 10 grams of adsorbents per 50 ml of adsorbate at the pH of 7 with 2 hours of contact time. This experimental condition can remove arsenic up to 41.39%. Experimental results are further used in Freundlich, Dubinin – Radushkevich, and Langmuir equations to understand the adsorption behaviors. The value of 1/n from Freundlich adsorption isotherm is 1.27, indicating that the surface of adsorbent is heterogeneous. The energy of sorption from Dubinin – Radushkevich adsorption isotherm is 3.79 kJ/mol, suggesting the kinetic is physical adsorption. In addition, the maximum capacity of adsorbent from Langmuir adsorption isotherm is 0.45 mg/g. Adsorbents are further tested with natural groundwater from 11 wells in Amphoe Dan Chang, Suphan Buri and Amphoe Ban Rai, Uthai Thani which contain arsenic ranges from 16.13 to 362.3 µg/l and have pH ranges from 6.95 to 7.35. After submerging 10 grams of adsorbents into 50 ml of contaminated groundwater for 2 hours, arsenic can be effectively removed between 20.17% and 75.31%. The variable amount of arsenic removal is likely due to the presence of phosphate, which has a similar structure to arsenite. In addition, the disintegration of adsorbents may release a noticeable amount of magnesium, which in turn inhibits the adsorption of arsenic and decreases the arsenic removal percentage.