Improvement in Arsenic Adsorption and Calcite Dissolution Kinetics through Size Reduction of a Ferric Hydroxide-Calcite Adsorbent

Abstract

The employment of granular ferric iron-(oxy)hydroxides, a well-known economic and effective method, lowers arsenic concentrations in different water types. However, for direct application in polluted groundwaters, there is a need to develop new injectable adsorbents for aquifers that could also neutralize acidic media. In this context, a granular ferric hydroxide-calcite (GFH-C) adsorbent was size-reduced to 0.4–50 µm by sonication with the aim of improving (i) the adsorption of As(III) and As(V) at different pHs and (ii) the pH control through the dissolution of calcite. Batch experiments were conducted to determine As(III) and As(V) adsorption isotherms and kinetics, as well as calcite dissolution kinetics, using GFH-C of two sizes (granular and sonicated). Results showed that the arsenic binding capacity of sonicated adsorbents did not improve significantly. On the contrary, the As(III) and As(V) adsorption kinetics improved with the sonication, as in the case of calcite dissolution kinetics. The dissolution of calcite from the adsorbent made the water pH increase to around 9.2–9.4. The sonicated adsorbent offers an advantage in depolluting As-containing groundwater due to its smaller size, which is linked with faster arsenic adsorption and effective acidic water neutralization.