pH-dependence Test Study on the Release of Heavy Metals in Cement Product from Co-processing Waste in Cement Kiln

Clinker was prepared by simulating cement calcination,which was used to produce concrete samples and crushed into particles with diameter 1 mm.The impacts of pH on the leaching behavior of heavy metals (Cr,Ni,As,Cd and Pb) and the ANC (acid neutralizing capacity) in crushed concrete samples were studied using the pH-dependence test.The results showed that the ANC of the concrete was large enough that it needed an addition of 2.5 mol/kg nitric acid to make the pH drop to 6.87 from lixiviating solution and 15 mol/kg nitric acid was needed to reduce the pH to 1.46.This was the reason that the pH of the pore water in the concrete was neutral or weakly acidic after a long time.The acidity and basicity of the leaching reagent were important factors impacting the leachability of heavy metals from concrete.In the investigated pH range,different heavy metals had different leaching characteristics.The leaching behavior of the heavy metals related to their forms in concrete and the adsorption of concrete minerals to heavy metals.