Cement Based Solidification/Stabilization Leaching Performances of Selected Heavy Metal Ions under Different pH Extractions

Abstract

bstract- Liquid to solid partitioning as a function of pH leachingProcedure LSP EPA method 1313 was carried out to test theeffectiveness , performance and efficiency of the cement-basedsolidification / stabilization (S/S) of heavy metals contaminated sandsamples using Ordinary Portland Cement OPC type A . Two cementbased mix designs ( 7 and 25 % ) have been applied to (S/S) sandcontaminated samples with different heavy metal ions ( Pb , Cu , Cr , andCd ) having the following concentrations ( 500 , 1500 and 3000 mg / kg). Fixed water to cement ratio of 0.45 was maintained for all theexperiments. Effective retention levels for the heavy metal ions wasachieved using a 25 % OPC mix ratio to (S/S) the contaminated sampleseven when the extraction solutions were of pH levels as low as 2.Leaching experiments showed that as the pH level of the extractionsolution is reduces and as the OPC content in the (S/S) samples is reducedthe more heavy metal ions that can leach out. Up to 80 % of chromium,cadmium, lead, and copper ions leachability can be prevented whenhigher cement content is introduced to the solidification / stabilizationprocess under the same pH extraction. Acidic extraction effects andsolubilized the Calcium – Silica – Hydrate (C-S-H) gel that is created bythe OPC binder, which holds, and contain the heavy metal ions and thusresults in more release of those ions into the extraction solutions. Thealkaline environments provided by the cement binder are believed to haveparticipated in the precipitation of several metal ions such as cadmiumand lead io, leading to their less detection in the leaching extracts.Alkaline extraction experiments (pH 8-13) showed that the mobility of themetal ions under the same experimental conditions followed the order ofpb> Cr > Cu > Cd in samples of various cement contents