Remediation Mechanism Research Of Chromite Ore Processing Residue By Pyrolysis Process With Biomass

Chromite ore processing residue (COPR) is a great environmental problem inChina. There are20chromium salt factories producing COPR now and most of theCOPR deposits without cover.COPR accumulative deposit has attained about300million tons.When it rains,the hexavalent chromium will be leaching and it results insoil and groundwater contamination. The Cr(VI) in COPR is one of the8mosthazardous chemical substances for human healthy and one of the three carcinogenicmetals international recognized.Co-pyrolysis was evaluated to treat COPR as a newkind of method.In this process,COPR and biomass were mixed together andpyrolyzed at high temperature. This process can be effectively to Cr(VI)reduction.However,the mechanism of reaction is not clear.In this paper, pyrolysismechanism of biomass components has been study,which provided a new theoreticalbasis for high efficiency energy saving technology.In this study, variables such as cellulose and lignin dosage, pyrolysis time andpyrolysis temperature were examined on the Cr(VI) reduction in COPR. Subsequently,through the analysis to Arrhenius kinetics equation as well as Gibbsthermodynamic,the study contrasted remediation pyrolysis mechanism of COPR withthe two kind of biomass. Provide theoretical guidance for the pyrolysis process.Themain results are listed below.(1)The removal rate of Cr(VI) increased while the temperatureincreasing.Volatile organic compounds release rapidly at high temperature.The longerreaction time lasts,the more complete it will react.The reaction stabilized after10minutes.Change the proportion of biomass has less affected on pyrolysis reduction ofCOPR. Two kinds of biomass components have obvious different effect at lowpyrolysis temperature,while a small difference above400℃. Cellulose’s pyrolysiswas slowly and poor reducing effect. Components of biomass has different ways tovolatile while in different pyrolysis characteristic,it was the most important reasonwhy different effects appeared.(2)The final disposal of Cr(VI) in the sample are always residue, and the amountof residue is different under different temperatures.It can be thought of that oxide formed on the surface of COPR will wrap part of Cr(VI) after long-termstorage.Organic volatile can not contact directly with this part of Cr(VI) at a shorttime pyrolysis.(3)The reaction of cellulose/Lignin and COPR were in line with first orderreaction has be established by kinetics experiment.The activation energies of cellulosereduction Cr(VI) is about17KJ/mol, and the activation energies of lignin reductionCr(VI) is about26KJ/mol.According to Arrhenius relationship at400℃,there is muchhigher number of activation molecules from cellulose than lignin.(4)By fitting the pyrolysis reaction of several main product of biomass volatileand COPR，draw a conclusion with Gibbs function changes that in each reaction, thepossibility is very large and react thorough at300K~1000K.