| Combined with the project "The study of existing state of Chromium in sludge from waste water treatment in steel factory and its mechanism of conversion" funded by the State Key Laboratory of Pollution Control and Resources Reuse, this dissertation studied the feasibility of Chromium recovery from steel factory waste water sludge. It is difficult to separate Cr (Ⅲ) from Iron by acid dissolution, but if chromium in sludge can be oxidized to chromate, then it can be easily dissolved in an alkaline solution, while iron and zinc remain precipitates. And the calcination is a possible approach.The existing state of Chromium, Iron, Zinc can be obtained through the XRD analysis of dried sludge. In order to provide the alkaline atmosphere which is a necessary condition in the oxidation of Cr(Ⅲ) to Cr(Ⅵ), glass fragment or sodium carbonate are added to the sludge during calcination. The influence of the quantity of glass fragment or sodium carbonate added on the chromium recovery is studied to obtain the optimal mass ratio of the glass fragment or sodium carbonate to the sludge. The optimal technical conditions are obtained through a series study of the effect of calcination time, calcination temperature, the extraction time, the extracting condition on the chromium recovery.Finally the result turns out to be: the calcination with sodium carbonate as an additive can oxidize most Cr(Ⅲ) to Cr(Ⅵ), the rate of chromium recovery can reach 60%, while at the same time the extraction rate of iron and zinc both remain below 1%. Between the calcination temperature of 600 - 1100℃, the glass can nott help to oxidize Cr(Ⅲ) to (Ⅵ) while sodium carbonate can, and to an certain extent of quantity added, the rate of Chromium recovery increase with the quantity added increase. The calcination time and calcination temperature are important to the ration of chromium recovery. Calcination time and calcination temperature are interactional, when the calcination temperature is higher, the time required for achieving the chemical balance is less, and the calcination period needed is less. Considered hightemperature need extra heating facility, so the calcination time and the calicination temperature are recommended to be 1 - 4 hours and 700—800°C respectively. The extraction time makes little difference in the ration of chromium recovery. From 20min - 24 hours, the rate of chromium recovery remain the same level, so the 10-2 minutes is choosed as the optimal extraction time. When the pH of extraction above 10, the pH's difference does not influence the rate of chromium recovery, however it will make the rate of Zinc extracted vary a little. The product of calcination has a little buffer capacity and the pH difference of deionized water and the O.OOlmol/LNaOH make tiny difference in the rate of chromium recovery. So the deionized water is recommended to be extracted solution. The L/S will influence the rate of Zinc extracted and the concentration of chromate in the solution, take these into consideration, the L/S is suggested to be 10.At last, the residu remained after the extraction was analyzed, the main composition was Fe2C>3, and it can be used as raw material to make desulfurization.
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