Treatment and Recovery of Chrome from Electroplating Wastewater (By Chemical Precipitation) ( At Homicho Ammunition Engineering Industry)

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Addis Ababa University


the reduction process of hexavalent chromium from electroplating wastewater by chemical precipitation in order to achieve the maximum trivalent chromium concentration. Sodium bisulphite is one of the widely used coagulants in waste water treatment process and has good reducing ability. Because of its reducing capacity, sodium bisulphite is applied to reduce hexavalent chromium from electroplating wastewater. The study has been conducted in four phases. In phase one reduction of hexavalent chromium, phase two determination of hexavalent chromium, phase three precipitation of chromium sulphate followed by oxidation of the sludge of Chromium (III) hydroxide. Phase one study was carried out to analyze the reduction process of the toxic soluble hexavalent chromium by using the concept of design experiment to justify the number of affecting factors and levels during the laboratory work followed by the synthetic waste sample preparation at Homicho Ammunition Engineering Industry in Ambo. Different experiments were considered like classical method of analysis to quantify and qualify the wastewater sample, atomic absorption spectrophotometric technique was utilized to determine the amount of total chromium, and finally colorimetric method to determine the amount of hexavalent chromium with a suitable complexing agent to engulf the ionic hexavalent Chromium. The total numbers of experiments were fifty four (54), the first twenty seven (27) run was analyzed by labeling the distributed parameters in each beaker of the solution and the number of factors with their levels were indicated. For the purpose of optimization of the selected parameters experiments were replicated, then at the second round of the experiment run number 44 was the optimized one. In order to perform these activities, the concentration of the stock solution was 100 mg/L, and 50 ml of volume was taken to each 500 ml beaker volume with concentration of 10 mg/L. With this amount phase two was conducted, to solidify the solution containing chromium sulphate Cr2 (SO4)3 generated from the redox reaction. . The required reduction time to reach equilibrium, the effectiveness of pH value for Cr (VI) reduction and the required amount of sodium bisulphite to complete reduction were investigated. The redox reaction was completed within 40 minutes, at pH of 2 and 50 mg/L of hexavalent chromium was reacted with 200 mg/L of sodium bisulphite in deionized water. Sodium hydroxide was used to precipitate the solution after the reaction of the precipitating agent and hexavalent chromium. In Final phase oxidation of Chromium (III) hydroxide to hexavalent chromium was carried out; Key words: Cr (VI) reduction, Sodium bisulphite, wastewater treatment



Cr (VI) Reduction, Sodium Bisulphite, Wastewater Treatment