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Study On The Preparation Of Light Rare Earth Oxide From Rare Earth Chloride Roasted Statically

Posted on:2011-03-07Degree:MasterType:Thesis
Country:ChinaCandidate:L XiangFull Text:PDF
GTID:2231330395958492Subject:Chemical Engineering
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There are two major parts on production of rare earth oxide in industrial process nowadays. First, rare earth carbonate or rare earth oxalate is produced by using ammonium bicarbonate or oxalic acid from rare earth chloride solution through extraction separation. Second, rare earth carbonate or rare earth oxalate will transform to rare earth oxide at high temperature (1123K). The first process generates waste water which contain much oxalate and ammonia nitrogen. The second process generates much carbon dioxide when roasted rare earth carbonate or rare earth oxalate. Those two processes would arise some serious issues. For one thing, it would cost much money to recycle raw material. For another thing, it would lay a potential influence on the environment. This paper have explored the thermodynamics, preparation and roasting process, thermal analysis kinetics and roasting process kinetics of rare earth oxide produced from direct roasting of light rare earth chloride, and expecting to completely change traditional process through further study.The chemical reaction of chloride of La, Ce, Pr and Nd which have the water of crystallization utilize direct roasting was studied detailed by using DSC-TGA and XRD methods. The results indicated that the temperature of dehydration of La, Ce and Pr is523K, Nd is673K. The chloride of La, Pr and Nd generate REOC1in first stage when roasted, and as temperature rise, Pr and Nd generate to oxide. Cerium oxide generated directly from cerium chloride at673K. But La can’t transform at1473K.Calculated the chemical reaction free energy of chloride of La, Ce, Pr and Nd which have the water of crystallization, and comparing with La, Ce, Pr and Nd, and know that the temperature of direct roasting reaction have the order that CeCl3<PrCl3<NdCl3<LaCl3. The free energy of liquid chloride is smaller than solid chloride. It have been demonstrated from that the conditions of thermokinetics would valid if dynamic roasting way of rare earth chloride actualized.By kinetics analysis of roasting process can be know that the activation energy of the reaction of cerium chloride is25.836kJ/mol, pre-exponential factor is0.706. The reaction is inner diffuse control, kinetic equation is1-(2/3)α-(1-α)2/3=0.706exp(25.8361RT)t. The apparent activation energy of the reaction of praseodymium chloride is132.479kJ/mol, pre-exponential factor is664.390. The reaction is chemical reaction control. And kinetic equation is1-(1-α)1/3=664.390exp(132.479/RT)t. The activation energy of the reaction of neodymium chloride is181.544kJ/mol, pre-exponential factor is21451. The reaction is chemical reaction control. And kinetic equation is1-(1-α)1/3=21451exp(181.544/RT)t.Static roasting experiment was studied on the basis of the thermodynamic and the kinetics research. The result proved that ceria was generated at673K, reaction ratio can be reached to98%when roasted30min at1073K. And the average grain diameter can be reached to2.108μm. When the roasting temperature reached1473K, the ceria turned to another type of crystal of ceria, and the average grain diameter increased. The temperature of reaction of praseodymium chloride and neodymium chloride was1223K and1323K respectively.According to the results of production of rare earth oxide from rare earth chloride through direct roasting, we may draw the conclusion that the plan with the virtue will being practical. The results of direct roasting will be optimized if dynamic roasting applied.
Keywords/Search Tags:Static roasting, rare earth chloride, rare earth oxide, preparation, kinetics
PDF Full Text Request
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