| The treatment process of Chromium-containing wastewater and sludge have been the focus of heavy metal pollution prevention. At present, there is a variety of ways for this pollutant disposal, and each method has its advantages and disadvantages. The way of trivalent chromium electro-deposition to obtain the sedimentary layer of chromium in simulated wastewater containing chromium can be an efficient way to achieve chrome recycle use.Firstly, we analysis the factors about the deposition of metallic chromium layer in different current densities (60,120,180,240A·dm-2) and pH (1.2,1.6,2.2,2.8) in chromium chloride solution when the trivalent chromium concentration is 20 g·L-1. The result shows that energy consumption is the lowest under the current density of 60A·dm-2 and pH2.8. The low current density is beneficial for the electro-deposition of trivalent chromium.The polarization behavior of working electrode was explored through polarization curve at the scan rate of 10 mV·S-1 with the potential range -2V (Ag/AgCl) from 0V(Ag/AgCl). From polarization curve of working electrode, it was found that the concentration of trivalent chromium participated on the surface of electrode is decreased with reducing of trivalent chromium concentration in electrolyte.The chromium deposition layer can be obtained in both chromium chloride and chromium sulfate solution, when trivalent chromium concentration is 20,10,8g·L-1, pH1.5 and pH2.5. With the trivalent chromium concentration decreasing, chrome crystal nucleus became smaller. The particals of chromium are larger under high concentrations. The lower concentrations of trivalent chromium is, the smaller and more intensive chromium nucleus is. The sedimentary layer was mainly consist of Cr(0) confirmed by Energy Dispersive Spectrodmeter (EDS) and X-ray Photoelectron Spectroscopy.Chromium deposition layer obtained in electrolyte of chromium chloride was obvious irregular and lamellated, when the concentration of trivalent chromium is 4g·L-1,2g·L-1,pH1.5, pH2.5 at the current density of 40A·dm-2,2 OA·dm-2. The sediment of the surface contains higher oxygen than the sediment of bottom does. The deposition layer is consist of large amounts of hydroxyl polymer generated adsorbed on the electrode in the reaction process, as pH increased sharply. Deposit obtained in electrolyte of chromic sulfate has metallic luster and the shape of chromium crystal nucleus tend to be uniform. Reduce the current density to 20A·dm-2, it can be found titanium electrode surface sediments are mostly nano-chromium particles. The deposition amount in electrolyte of chromium chloride is less than it in electrolyte of chromic sulfate.It can be found that the deposit obtained in the electrolyte of chromium chloride mainly consist of Cr(III), may be due to chromium hydroxyl polymerization generated and Cr2O3 or other Cr oxide after EDS and XPS detection. Chromium deposit obtained from chromium sulfate is mainly in the form of Cr(0). It is difficult to obtain chromium deposit after change pH of electrolyte and current density when the chromium concentration is lg·L-1。It shows that the higher concentration of trivalent chromium can make the electrode surface absorbed more trivalent so as to inhibit hydrogen evolution reaction on the cathode surface, when the trivalent chromium concentration was maintained in the higher range 8g·L-1 from 20g·L-1 ,It results to a little changes of pH so that little hydroxyl polymer of chromium generated. When the chromium concentration is low, the solution of hydrogen evolution reaction is strong which lead to hydroxyl polymer of trivalent chromium generated more. When solution of trivalent chromium concentration increased, the current efficiency was also increase, because of more trivalent chromium compete with hydrogen ions for electrons in the reaction, so there are more metallic chromium generated. As chromium concentration less than 4g·L-1 the chromium deposition efficiency decreased. The main reaction in the surface of electrode is hydrogen evolution.It can be found that sodium formate can be better formed complex with chromium in the solution of trivalent chromium with chromium powder as the source. It will obtain satisfactory deposition layer as pH2.5 and the current density of 20A·dm-2. With spacing increasing between two electrodes, the deposition amount added. From tanning wastewater can be also obtained chromium deposition. After stirring and adding hydrogen inhibitor will reduce the pH changes in the electro-deposition process. |
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