| During the leather process, retanning dyeing wastewater contains heavy metal chromium and various remained organic matters, and they can interact with each other resulting in more complex form of trivalent Cr(III) which is hard to be removed with conventional treatment technology. In this paper, alkaline precipitation method with the cooperation utilization of coagulant was applied to the treatment of chromium in practical retanning dyeing wastewater from different factories. Acrylic resin tanning agents RF, RV and PS were chosen and the interaction of them with Cr(III) were studied as well as the stability of the Cr(III)-tanning agents system. In addition, the interaction of two nano-polymer tanning agents with Cr(III) and the effect of them on the precipitation performance of Cr(III) were also investigated. The results showed that:1.when alkaline precipitation method with the cooperation utilization of coagulant was applied to the treatment of retanning dyeing wastewater from a tannery factory in Hebei Province, the removal efficiency related a lot to the type of precipitant. When slaked lime was utilized with the cooperation utilization ferrous sulfate as coagulant, total chromium content of the final effluent could eventually meet discharge standard(1.5mg/L). While when the same method was applied to the treatment of five kinds of retanning dyeing wastewater of different technologies from a tannery factory in Zhejiang Province, the total chromium content of only one type of final effluent could eventually meet discharge standard. And even the removal of total chromium of other four were all higher than 80%, the total chromium content could not meet discharge standard.Therefore, the alkaline precipitation method could not effectively remove the total chromium in retanning dyeing wastewater from different technologies to ensure meeting the discharge standard.2.We characterized their structure and properties by infrared spectrumanalysis, nuclear magnetic resonance spectroscopy, gel permeation chromatography analysis, ultraviolet-visible spectra representation, and the determination of their Zeta potential.3.We studied the range of complexing point of three kinds of acrylic resin tanning agents with chromium. The result was: 0.3-0.35ml;RF,0.15-0.16ml;RV,0.15-0.2ml.The three kinds of leather chemicals all could combined with Cr(III). When the acrylic resin retanning agents were exceeded,there were no obvious precipitate of Cr(III) during the p H of 3-13.And the turbidity was little with little vary.When the acrylic resin retanning agents were not enough to Cr(III), their influence on Cr(III)-retanning agents were different. With less RF,the stability of solution system was the worst at the p H of 4.5.Then with the increasing of p H,the stability got better.With less PS, the stability of solution system was the worst at the p H of 5.With less RV, the stability of combing system was worse at the p H of 4-8 and it was easy to be precipitate. With less three kings of acrylic resin retanning agents, the solution p H all had a mutation process with alkaline increasing.Knowing from the ultraviolet-visible spectra varied with the increasing of p H, we studied that with the addition of RF and PS, the characteristic absorption peak first went to blue shift and then went to red shift. While after interaction of RV and Cr(III), the characteristic absorption peak only went to red shift.4.The ability of combing the two new kinds of nano polymer tanning agents with Cr(III) had great relation to their own synthesis methods which had obvious effect on the stability of Cr(III).We found that the two nano polymer tanning agents compound bound with Cr(III) which made the Cr(III) concentration decreased. However because of high dispersion, even under the alkali precipitation optimum p H range,existing the suspended state chromium in solution made it difficult to meet the national standards. |
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