Impact of pH on the Release of Cr in Cement Product from Co-processing Waste in Cement Kilns

Clinker was prepared by simulating cement calcinations,which was used to produce concrete samples.The impact of pH on the release of Cr in the concrete samples was studied using the EA NEN 7375 method by five leachants with different pH.The results showed that the cumulative release amount of Cr in the concrete was great under the strongly acidic conditions;the release amount reached 64.7 and 21.4 mg/m2 when the leachant pH was 2.00 and 3.50,respectively.However,the cumulative release amounts of Cr were low and similar when leachant pH was 5.00,7.35 and 10.00,reaching and was 5.10,5.05 and 5.00 mg/m2 when leachant pH was 5.00,7.35 and 10.00,respectively.Diffusion control was the main release mechanism of Cr in the solutions with pH 5.00,7.35 and 10.0.The release curves well fitted the standard line well with slope 0.5,and slopes of different increments ranged 0.35-0.65.When leachant pH was 2.00,diffusion control was the main mechanism of Cr at the early stage,while depletion occurred at the later stage.A similar phenomenon was observed at the early stage when leachant pH was 3.50,but dissolution occurred after the middle stage.