Calcium Polysulfide Treatment Of Cr(â…¥)-contaminated Groundwater

The groundwater pollution is critical as the economy and society. Chromium isan important chemical material, it’s toxic to human and are difficult to biodegradation.Due to chromium-contaminated waste water discharging and the chromium oreprocessing residue piling up without restraint, chromium is poured into thegroundwater in great amount. Chromium is toxic, carcinogenic in its hexavalent form(Cr(Ⅵ)), research on the groundwater chromium management and treatment is ofgreat significance.Calcium polysulfide (CaS5)-In situ treatment has been found to be a promisingtecqiue to deal with the chromium contamination. It does little destabilization to theunderground environment, the simple operation, highly safety and less investment arealso advantages of this technology.Recently, it gets high attention all over the world.The object of this article is to study the factor of chromium contained groundwater bycalcium polysulfide, the mechanism of the chromium reduction and the further studyof dynamic experiment of chromium treatment by calcium polysulfide, which canprovide theory direction to the actual groundwater treatment. Results showed asfollow:(1)The optimization dosage of CaS5was3multiples as the chromiumconcentration, the effluent concentration of Cr(Ⅵ) can reach to III class of Qualitystandard for groundwater GB/T1448-93, even increasing the dosage of calciumpolysulfide,the chromium removal is out of variance;(2)With the end of the reaction, the pH and Eh value was8.64and279.9mV,which was higher the beginning; the physical and chemical properties of groundwatermade a bigger change. The neutral, acidulous and high environment temperature canshorten the reaction time of the chromium removal;(3)When the chromium contaminated groundwater also contained Mn2+or Fe3+,the chromium reduction velocity was accelerated; but the existence of SO42-or NO3-,there was of no use to the reaction process; when the high concentration of HA wouldsuppress the reaction. More, CaS5can deal with high salinity and high alkalinity chromium contaminated water;(4)To explore the mechanism of CPS reduction with chromium, the XRD andXPS spectrum analysis status demonstrated the precipitates of the reaction wereCaSO4, S and Cr(OH)3;(5)The dynamic research on the removal rate of chromium using calciumpolysulfide was the principal content in this article. Results indicated that: theoptimum dosage was3multiples as chromium concentration to inject calciumpolysulfide into the column, the effect distance can be60.00cm, Cr(Ⅵ) effluentconcentration was under the standard of GB/T1448-93Groundwater Quality ClassIII(0.05mg·L-1), the persistent time was very long, the effect of the injection to theaquifer pH and Eh was very small, the max concentration of Ca2+and SO42-were bothfar away from the GB/T1448-93Groundwater Quality Class III(450mg·L-1,asCaCO3,250mg·L-1); the change of aquifer permeability coefficient must pay attentionafter the injection.