Assessing arsenic leachability from pulverized cement concrete produced from arsenic-laden solid CalSiCo-sludge

Synthetically prepared arsenic-laden CalSiCo-sludge was converted to pulverized cement concrete (PCC) using solidification/stabilization technology with cement. Batch leaching experiments were conducted to estimate the leaching of As(III) and As(V) from the CalSiCo-sludge as well as from the PCC. The leaching of As(III) and As(V) was found to be the function of time, pH and concentration of anions such as Cl(-), NO(3)(-), and SO(4)(2-) present in the extraction fluid. It is observed that from the CalSiCo-sludge the leaching of As(III) is >0.05mg/l (which is above the permissible limit for arsenic in drinking water) at any pH. But in case of As(V) the leaching is >0.05mg/l only at pH>8 and at pH<4. It is noted that maximum leaching occurs when the extraction liquid contains Cl(-). In contrary, NO(3)(-) and SO(4)(2-) have negligible effect on arsenic leaching from the CalSiCo-sludge. Extraction tests were carried out to determine the maximum leachable concentration under the chosen conditions of leaching medium and leaching time. Leaching of As(III) and As(V) from exhausted arsenic-laden CalSiCo-sludge and from PCC was carried out in both tap water and rain water. It was noticed that tap water has no effect in leaching of arsenic from CalSiCo-sludge but rain water causes significant amount of leaching, which is mostly due to pH effect. However, in all cases the leaching of As(III) was more than that of As(V). When compared with CalSiCo-sludge PCC showed negligible leaching of arsenic. It was noticed further that the variation of 28 days compressive strength was within 15% of the original strength after replacing 35% cement with exhausted CalSiCo-sludge.