Study Of Phosphate And Chrome In Waste Water Using Reduced Chromium Slag

Chrome pollution is a great environmental problem in China. There are many shortages in the treatment and disposal methods. Pyrolysis has becoming a promising treatment method in hexavalent chromium containing solid wastes, and has some advantage in chromium slag treatment. But there will be secondary pollution if the residual has not been treated well.The environmental safety of the reduced chromium slag pyrolysised under 600℃and 800℃has been proved. Then the reduced slag were used in treatment of phosphate and Cr(Ⅲ) in waste water. The effects of some factors, such as dosage and pH were investigated with the mechanisms of phosphate removal and Cr(Ⅲ) removal discussed, which provided a new solution for reutilization of reduced chromium slag.The results showed that the consist of chromium slag did not changed much during pyrolysis process, Cr(Ⅵ) has been reduced to Cr(Ⅲ). The leaching toxicity reduced dramatically. Chromium speciation results indicated that the pyrolysis process stabilized the chromium in the slag. The reduced chromium slag has a strong acid buffering capacity of over 10mol/kg. The column leaching study and long term performance testified the stabilization of reduced chromium slag and indicated the feasibility of reutilization of reduced chromium slag.The result of phosphate removal indicated that the treated samples had an effective treatment performance on phosphate removal. At the dosage of 600℃and 800℃reduced chromium slag 2.5g/L and initial phosphate concentration of 50mg/L, the removal rate can reach to 50.1% and 99.0% respectively. The pH of the water can affect the removal rate obviously. Effect of coexisting ions on phosphate removal showed that the NO3- and SO42- as electrolyte can enhance removal rate. HCO3- can facilitate phosphate removal at low concentration while inhabit removal at high concentration. The coexistence of Ca2+, Mg2+ and NH4+ can enhance phosphate removal.Reduced chromium slag had a great removal efficiency both for high and low Cr(Ⅲ) containing waste water. When the dosage is 2.5g/L, the removal efficiency is over 95%. The result showed that the removal of Cr(Ⅲ) was due to precipitation. The residual precipitated better with more dosage of slag, and can be used as chrome ore.