Study on treatment of high concentration chromium-containing waste liquid with modified iron preparation and recycling of chromium-containing iron
The recycling of chromium faces many problems in waste liquid treatment,such as low chromium contents and high impurity amounts in treatment sludge.Sulfide-modified Zero-Valent Iron(S-ZVI)and organic acid were employed as the purification agent for chromium waste liquid.With the efficient removal of chromium in the waste liquid,the ferrochrome alloy can be directly prepared by purifying the sludge.The effects of key factors such as the sulfidation degree of zero-valent iron,pH value of initial waste liquid,proportion of organic acid,and dosage of S-ZVI on the purification of waste liquid chromium and the enrichment of chromium in sludge were investigated.The direct preparation of chromium alloy from chromium sludge was explored.The results show that the optimal reaction conditions are as follows:the molar ratio of n(S)/n(Fe)was 0.116,the total concentration of organic acid was 12 mmol/L,n(C4H6O6)∶n(C6H8O7·H2O)=3∶1,adding iron mineralizer w(Cr)/w(Fe)=0.11.The total chromium of waste liquid can be reduced from 5 324.1 mg/L to 4.30 mg/L.Compared with the unmodified zero-valent iron,the removal rate of chromium can be increased from 65.45％to 99.92％.The contents of Na,O,and other impurity elements in the sludge are about 50％,much lower than that in conventional sodium bisulfite reduction sludge(about 69％).The average content of chromium element in the sludge is＞46％,which is easy to be recycled.The result shows that ferrochrome alloy was successfully prepared by adding carbon powder with a mass fraction of 30％under 1 500 ℃ and an argon protective atmosphere.XRD analysis shows that the impurity in the alloy products can be reduced with the increase of the addition of S-ZVI SEM-EDS analysis shows that the ferrochrome products are evenly distributed with fewer impurities.The carbon consumption amount is only 66.7％of the previous technology,which provides a new path for the green and low-carbon recovery of chromium in hazardous waste.
environmental engineeringhigh mass concentration of chrome-containing waste liquidorganic acid-iron mineralizerreduction precipitationchrome-containing sludgeferrochrome alloy
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