Study On The Chemical Speciation Analysis And Recycling Of Chromium In Tannery Sludge

In this paper,the tannery sludge used as the research sample was collected from a tannery in Binyang county of Guangxi province.The basic properties(moisture content,organic matter content,pH,total chromium content,hexavalent chromium content)of the sludge were been researched.The speciation distribution of Cr in sludge was studied by Tessier and BCR sequential extraction procedures.Vitamin C was adopt as a reductant to study and optimize the reduction conditions of Cr(?)in simulated tannery sludge samples.Chromium was reclaimed from tannery sludge by using oxidative roasting-water leaching method.The experimental results showed that:(1)The speciation distribution of Cr in sludge was studied by Tessier and BCR sequential extraction procedures.The results of BCR method showed that the predominant fraction of Cr in samples was the Fe/Mn oxide fraction(87%?88%)and the results of Tessier method showed that the predominant fraction of Cr was the oxidisable fraction(97%).Both of them have shown the proportions of other forms were low.(2)To study and optimize the reduction conditions of Cr(?)in simulated tannery sludge,Vitamin C was adopted as a reductant.The optimum reduction conditions of Cr(?)combined by single factor experiment,orthogonal experiment and economic factors were as follows:the dosage of Vitamin C was 1.5 times of the theoretial amount(according to the chemical reaction equation),pH was 2.0,the reaction time was 4 h,and the reaction temperature was 35 ?.The reduction rate of Cr(?)reached 82.2%under the above conditions.(3)Oxidative roasting-water leaching test was conducted to reclaim chromium in tannery sludge.The results indicated that roasting temperature is the most important factor influencing the leaching efficiency of Cr,followed by the leaching time,the dosage of Na2CO3 and the roasting time.The optimal operation conditions were as follows:the dosage of Na2CO3 was 1.0g/g,the roasting temperature was 600 ?,the roasting time was 1.5 h,and the leaching time was 1.2 h.Under these conditions,the percentage of total chromium in the leachate was 95.5%.By meas of reduction experiments,precipitation experiment and calcination experiments,the hexavalent chromium in the leaching solution recovered.The recovery rate achieved to 90%in the form of Cr2O3.