The Form And Distribution Of Heavy Metals During Co-processing Waste Contained At Different Temperatures

In order to discover the migration and patterns of heavy metals duringco-processing hazardous wastes in new dry ceme nt k ilns, we studied the residua l rateof Cr, As, Pb in the c linker, particulate matter and exhaust, che mical and extractionform in the calc ined clinker under different calc ination te mperatures. Na2CrO4、NaAsO2、PbO were mixed with cement production raw materials, and the mixtureswere burned under900℃、1000℃、1100℃、1200℃、1300℃and1450℃, respectively,to simulate the co-processing wastes us ing ceme nt kiln. The residua l rate of heavymeta ls was stud ied by digestio n of sa mp les calc ined. Simultaneous ly we detectedcontents of heavy metals in the absorb liq uid within the exhaust gas and ana lyzed themigration of heavy meta ls. The che mica l forms of Cr、As、Pb were obtained by X-rayabsorption near edge structure (XANES) and X-ray diffractio n(XRD). The extractionforms of Cr、As、Pb were obtained by Mod ified Tessier sequential extraction method.The results were as follows:The content of Cr in vo latile particulate matter was the largest at1200℃and theproportion is32.79%. While under900℃and1450℃, the distributio n proportion ofCr in exhaust gas was up to peak which both were0.24%. The residua l rate of Cr wasthe highest at the temperature of1100℃whic h was73.7%. As was also ma inlydistributed in the c linker at six temperature and distribution ratio were stable between81%and83%. At900℃,the fixing rate of As in clinker was the largest whic h was97%. At1450℃, the As concentration in the exha ust gas reached the maximum andthe proportio n was0.0023%. The residua l ratio of Pb in the clinker decreaedgradually as the temperature rised. While the concentratio ns of Pb in volatile partic lesand exha ust gas showed an opposite trend. The kiln tail of temperature was1050～1100℃and was closed to1100℃, therefore, it reduced the disposal o f Cr and Asduring co-process ing waste in the cement kiln adding waste at the kiln ta il.We shouldstrictly control amount of leaded waste into the kiln.Cr ma inly e xisted in the forms of CrO3,Cr2O3and CaCrO4under the conditio nsof900～1450℃.Cr combined with other substances entered into the main ceme ntmineral, whic h generate more co mple x Cr-containing substances such asCa4Al6O12CrO4and this materia l was ma inly in the form of CrO3and Cr2O3under theranges fro m1100℃to1450℃. Ca2As2O7ma inly exists in the clinker under the cond itions o f900℃. FeAsO4and Ca3(AsO4)2can be detected in the samp le calc inedunder cond itions of1000℃.Ca3(AsO4)2ma inly exists in the clinker under thecond itions of1100℃and existed in the forms of Ca5(AsO4)3(OH) under the cond itionsof1200℃、1300℃and1450℃. Pb2O3can be detected in the samp le calc ined Undercond itions o f900℃, Pb ma inly e xisted in the forms o f Pb6Al2Si6O21under thecond itions of1000℃and1100℃, Ca3PbSiO6can be detected in the samp le calc ined at1200℃, Pb cannot be detected in the samples calcined at1300℃and1450℃.K2CrO4（or Na2CrO4）is the perform of exchangeable.CaCrO4and part of CrO3and Cr2O3into the clinker minera ls showed acidic solution of sodium acetateextractable, acid extractable hydroxylamine hydrochloride solution and acid ichydroge n peroxide extraction state. The most of Cr inserted the ma in minera l C2S andC3S show resid ual. And the resid ual form is the ma in form.Ca2As2O7slightly solub lein water, soluble in d ilute acid, expressed as acid extractab le hydroxylaminehydrochloride solution and acid ic hydrogen peroxide extractable.FeAsO4showedac idic sod ium acetate solutio n was extracted state. The number of As cured by C2Sand C3S increase in the range of1200℃~1450℃and this part of As show residua l.Pb2O3inso luble in water, soluble in dilute acid and lye, expresses as acid extractablehydroxyla mine hydrochloride so lutio n. The form of Pb6Al2Si6O21is the residua lperformance. Ca3PbSiO6inserted C3S and C2S crystal lattice appears residua l.Disposal o f hea vy meta ls during co-processing hazardous wastes in new dry ceme ntkilns provide a theoretical basis to select the appropriate dosing points, the same time,the existing forms o f Heavy meta ls during co-processing ha zardous wastes in new dryce ment k ilns can be used to assess the potentia l environme nta l risks of ceme ntproducts.