The Recycling Technology Of Ferrum,Aluminum,Chromium In Chromite Ore Processing Residue

Chromite ore precessing residue?COPR?is the remaining tailings of chromite non-calcium roasting process,which is classified as industrial solid waste.However,it's also a potential secondary resource because of containing abundant metal elements with an annual output of six hundred thousand tons.Therefore,the recycle technology developing is not only the fundamental requirement of environmental protection and resource conservation,but also the urgent need for the sustainable development of chromium salt industry.A Water Washing-Acid Leaching-Flocculant Preparation process was proposed to efficiently utilize COPR based on its'physicochemical characteristics.In the water washing process,a atmospheric stirring leaching method was introduced to recover sodium chromate by using deionized water as a lixiviant.The results indicate that sodium chromate recovery reached 97.27%under the optimum condition namely,the liquid-solid ratio of 10 mL·g^-1,with 70°C,200 rpm and 33 min period.Simultaneously,the leaching kinetics of sodium chromate was successfully modeled by a classic shrinking core model with the liquid film diffusion as the rate-controlling step,where the apparent activation energy was decreased from 17.66 kJ·mol^-1 to 11.27 kJ·mol^-1with stirring rate increased from 50 rpm to 300 rpm.In the acid leaching process,a hydrometallurgy method was introduced to recover metal elements by using concentrated hydrochloride acid as a lixiviant and the optimum leaching parameters were at the liquid-solid ratio of 5.6 mL·g^-1 with 110oC and 6 h period.Under this condition,the extractions of chromium,ferrum,aluminum and magnesium reached 67.76%,89.89%,93.99%and 95.21%,respectively.Simultaneously,a shrinking core model with the surface chemical reaction control can be used to describe the leaching kinetics of chromium,ferrum,aluminum and magnesium from COPR in the concentrated hydrochloride acid solution at 90-110°C,where the apparent activation energy are 102.31 kJ·mol^-1,78.10 kJ·mol^-1,66.44 kJ·mol^-11 and 81.66 kJ·mol^-1,respectively.Furthermore,the activation energy for ferrum,aluminum,chromium and magnesium leaching were reduced to 60.44 kJ·mol^-1,61.61kJ·mol^-1,79.33 kJ·mol^-11 and 70.55 kJ·mol^-1,respectively,after pretreatment by mechanical ball milling.A alkalizing-polymerization method was introduced to prepare polyferric aluminum chloride?PFAC?from acid leaching solution.The coagulation performance was investigated by verifying the COD and chroma removal efficiencies in biochemical effluent treatment of landfill leachate.The results show that the optimum conditions for preparing PFAC were n_?NaOH?/V_{?acid leaching solution?}=2 mol·L^-1,c_?NaOH?=0.2 mol·L^-1,and aged at 70oC for 3 days,simultaneously,the optimum parameters for coagulation were pH=7.35,T=23oC,PFAC dosage 11 g·L^-1,and precipitation for 15 minutes.Under this condition,the removal efficiencies of COD and chroma were 76.33%and 83.54%,respectively.Furthermore,polysilicic acid was used to prepare poly-silicic-cation coagulant?PSC?for coagulation performance elevation and security guarantee.With the increasing dose of polysilicic acid,the removal efficiencies of COD and chroma were increased.And the optimal dosage was n_?PS?/V_{?acid leaching solution?}=0.4 mol·L^-1.Under this condition,the removal efficiencies of COD and chroma was 85.23%and 90.02%respectively.