The Study Of Removal Chromium From Chromium Slag Using An Improved Electrokinetic By Bipolar Membrane

Chromium slag is one kind of hazardous solid wastes generated as byproducts during the process of producing chromium salts.The electrokinetic technique has been regared as an effective method for treatment chromium slag due to high removal efficiency and environmental friendly.However,the discharge of it,such as low current efficiency and high consumption has limited its application.For solving above problems,a combined technique of electrokinetic and a bipolar membrane was used to remove chromium from chromium slag in this study,the main conclusions are as follows:A high current efficiency and low consumption were obtained when the electrolytic cell was equipped with more chromium slag chamber in series.Under the optimized experimental parameters of the pH value was 3.00,electrolyte NaNO3 concentration was 1.0 mol/L in the anode chamber,electrolyte HNO3 concentrations was 0.8 mol/L in the cathode chambers,and the current density was 3.0 mA/cm2,the removal efficiencies of Cr(?)in a three chromium slag chambers equipped system,were 88.5%,85.7%,and 95.8%,respectively,after 300 h.The specific energy consumption decreased to 0.395kW-h/g of chromium,and the current efficiency increased to 2.305%.It was found that the other heavy metals,such as Ca,had an obviously effect on Cr(?)removal when the system was used to remove Cr(?)from chromium slag.Under the optimized experimental conditions of the electrolyte HNO3 concentration was 0.8 mol/L in the anode chamber,electrolyte NaNO3 concentrations was 1.0 mol/L in the cathode chambers,and a current density was 2.0 mA/cm2,almost the same removal efficiency of Cr(?)in every chamber of three different setups were obtained.When a three chromium slag chamber equipped system was used to treat chromium slag,the removal efficiency of Cr(?)were 27.9%,15.7%,25.9%,respectively,after 288 h.Meanwhile,the specific energy consumption decreased to 0.033 kW·h/g of chromium,and the total current efficiency increased to 29.23%.The current efficiency can be obviously enhanced when a "back to back" chromium slag chamber equipped system was used to remove Cr(?)and Cr(?)simultaneously.When the pH value was 3.00 in chromium residue chamber,which closed to anionic exchange membrane of bipolar membrane,electrolyte NaNO3 concentration was 1.0 mol/L in the anode chamber,electrolyte HNO3 concentrations was 0.8 mol/L in the cathode chambers,and a current density was 2.0 mA/cm2,the removal efficiencies of Cr(?)were 75.6%,78.2%,85.0%,respectively;and that of Cr(?)were 29.3%,29.6%,24.7%,respectively,after 300 h in a three "back to back" chromium slag chamber equipped system.The specific energy consumption decreased to 0.070 kW·h/g of chromium,and the current efficiency increased to 39.129%.