1 A PILOT STUDY FOR ARSENIC REMOVAL FROM WATER BY ADSORPTION IN NATURAL ZEOLITE ADSORPTION IN PRESENCE OF IRON AND MANGANESE.

Abstract. The possibility of removing soluble arsenic from water during the application of a treatment for the removal of iron and manganese contained in that same water, has been reported by several authors. In spite of this, it is not yet possible to know in a precise manner the efficiency of removal to be accomplished in a specific case, which is why it is necessary to perform studies on a small scale with this objective. This work presents the results obtained in a pilot study performed on water from a group of wells that supply water to an important city in Mexico. The technology chosen for water treatment was the so-called natural zeolite adsorption-oxidation, which efficiently removes iron and manganese from water. In previous laboratory studies, it was also possible to prove the removal of arsenic through sorption, on this type of material. Most of the tests were performed with the mixture of water from several wells. Arsenic concentration varied between 0.021 and 0.032 mg/L, iron between 0.41 and 3.18 mg/L, and manganese between 1.1 and 1.3 mg/L. Total arsenic removal was between 19 and 60 %. The results show that the achieved arsenic removal is the sum of arsenic co-precipitation with iron, and the arsenic adsorption of manganese oxides that cover the zeolite. For a clean bed, arsenic adsorption of zeolite seems to be the main mechanism. However, as bed operation time passes, the sorbent material reduces its removal efficiency, leaving the most important role to co-precipitation. Tests were performed on two different water filtration velocities through the bed: 7.6 and 14 m3/m2h, the low velocity produced higher efficiencies, although the difference is not highly significan