Research On Removal Of Cr⁶⁺ From Passivation Wastewater By Polymer Complexation Ultrafiltration

There is a wealth of rare earths of Gannan region, of which mining, smelting andprocessing will produce some industrial wastewater containing a certain concentration ofheavy metals and organic pollutants. The wastewater that were discharged into thesurrounding water will cause the increase of heavy metals and reduction of dissolved oxygen,harming the survival of marine life. More seriously, people health will be hurt when heavymetals are drank into people body. One of the most fundamental treatment means is first toremove the heavy metal ions then biodegrade organic matter. This paper is mainly aimed atthe removal of Cr(Ⅵ) produced in the passivation and phosphate process of the production ofrare earth material and provides the premise for subsequent treatment processing of organicwastewater.With PAC, cationic PAM, PVA, PAAS and PEI as chelating agent to remove Cr(Ⅵ),respectively, this paper using PVDF hollow fiber membrane inspected five different effects ofCr(Ⅵ) removal and membrane fouling, then screened out the optimum one which wassuitable to treat the actual passivation wastewater. Then the optimization experiments wereperformed to study the effects of pH, the polymer/metal ions loading ratio, operatingpressure and other factors on the retention rate of Cr(Ⅵ) to further determine the optimumconditions. While Henry adsorption model, Langmuir monolayer model and Freundlichmodels were used to theoretically study Cr(Ⅵ) chelating model theory, and Langmuirmonolayer complexation model was found to be basically consistent with the experimentalobtained data.Through experiments, some following results were obtained.（1）PEI was chose the most suitable chelating agent to treat the actual passivationwastewater.（2）PEI showed good binding ability of Cr(Ⅵ) in the acidic conditions, and more badunder the condition of alkaline(pH＞8), while the removal rate slightly increased with theconcentration of PEI.（3）When P/M was7, the retention rate of Cr(Ⅵ) would not increase with the increaseof the concentration of PEI, thinking complexation reaction to measuring balance in P/Maround7. （4）With PEI as chelating agent, the retention rate of Cr(Ⅵ) in the actual passivationwastewater was lower than it in model wastewater.（5）The membrane flux almost linearly increased with the operating pressure.（6）The membrane flux gradually decreased and the retention rate increased in the top20min, then all remained stable.（7）When temperature was between15℃and30℃, the membrane flux almost linearlyincreased and the retention rate of Cr(Ⅵ) still remained stable at around85%; whentemperature was between30℃and40℃, the membrane flux presented a nonlinear increaseand the retention rate of Cr(Ⅵ) greatly reduced.