Abstract
In this paper, aiming at the problem of chrome-iron separation in electroplating sludge, the separation of ferrochrome by complexation and precipitation with benzoic acid as complexing agent is achieved. The optimal conditions consisted of a 1: 3 molar ratio of Fe3+: C6H5COOH, a reaction temperature of 30°C, a final pH of 2.5 and a reaction time of 2 min. The separation rate of the iron was 97.38% and the rate of loss of chromium was only 3.59%. The ferrochromium separation products were analyzed by XRD, fluorescence spectroscopy, infrared spectroscopy and H NMR Spectroscopy in order to study the mechanism of precipitation. The results showed that benzoic acid preferentially forms a complex with iron and iron benzoate precipitates with an increase pH. The iron benzoate crystals have a fine particle size, settle rapidly and are easy to filter. The separation of Cr 3+/Fe3+ was successful using our methodology.
Highlights
The electroplating industry in China produces approximately 10 million tons of electroplating sludge every year, which is classified as hazardous waste due to containing harmful substances, for example, chromium (Wei-hua and Xue-fu, 2006; Qiu-yue, 2014)
The results of our study provide a new method for the comprehensive recovery of chromium from mixed electroplating sludge
Effect of Solution pH on Ferrochrome Separation From the reaction Eqs. 1, 2 it can be shown that the coordination between benzoic acid and iron and chromium ions is affected by the pH of the solution
Summary
The electroplating industry in China produces approximately 10 million tons of electroplating sludge every year, which is classified as hazardous waste due to containing harmful substances, for example, chromium (Wei-hua and Xue-fu, 2006; Qiu-yue, 2014). Crystallization method and cupferron as a precipitating agent to separate chromium and iron successfully, but the processes are relatively complicated and the problem of secondary pollution cannot be completely resolved. A new method for the separation of ferrochromium by a selective complexation precipitation is achieved using benzoic acid as complexing agent which can form a insoluble complex with iron in aqueous solution. In the electroplating sludge leaching solution mixed with chromium and iron, the benzoic acid coordination agent which was used was that. The benzoic acid ethanol solution was slowly added dropwise to the mixed chromiumiron solution, and the pH was adjusted with ammonia water to achieve selective complexation and precipitation of the iron ions.
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