Effect Of PH Value On Leaching Behavior Of Rare Metals From Red Mud

Red mud,as the tailings residue of alumina industry,is accumulated in the field by wet method.Due to the strong alkaline salts and heavy metals,red mud will pollute the surrounding soil,surface water and groundwater environment.On the other hand,because the red mud has good adsorption properties and contains rich rare metal resources,it can be used as a new environmental engineering material or metal resources for secondary recovery,so as to achieve the purpose of resource utilization.At present,a lot of research has been done on the recovery and utilization of rare metals in red mud all over the world,but there are few studies on the leaching behavior of rare metals in red mud under different pH conditions.In this paper,red mud samples from five different aluminum plants in Guangxi,Henan and Shandong were used as research objects.The leaching rate and leaching behavior of five rare metals in red mud under full pH condition were studied by geotechnical experiments,chemical composition experiments and fixed pH leaching experiment combined with geochemical equilibrium model.The following conclusions were obtained:(1)The mineral composition,chemical composition and chemical element composition of five kinds of red mud were studied by means of quantitative X-ray diffraction,X-ray fluorescence spectrometry and combined digestion of four acids.The results show that the moisture content of five kinds of red mud is high,and the particle sizes are distributed among 0.075mm-2mm.The main mineral compositions include quartz,calcite,hematite,garnet,sodalite,anhydrous gypsum,calcium nepheline and trihydrate.The main chemical compositions are SiO₂,TiO₂,Al₂O₃,Fe₂O₃,CaO and Na₂O,and the main elements including Al,Ca,Fe,Na,Ti and Si.(2)EPA Method1313 sequencing batch fixed pH leaching method was used to study the leaching characteristics of rare light metal Li,Rb,rare earth metal Sc,Y,La,Ce,rare refractory metal V,Mo and rare dispersed metal Ga in five kinds of red mud at fixed pH value.The results showed that the natural pH value of the five kinds of red mud are in the range of 10.5-11.0.The acid neutralization capacity curve obtained in the leaching experiment shows that the five kinds of red mud samples are easily affected by acid conditions.The analysis of ion leaching mode shows that rare light metal Li,rare earth metal Sc,Y,La and Ce are cationic leaching mode,rare light metal Rb,rare refractory metal V and rare dispersed metal Ga are V-shaped amphoteric leaching mode,and rare refractory metal Mo shows anion leaching mode.(3)The geochemical equilibrium model was used to study the leaching behavior of Sc,Ga,V,Li,Rb and Mo in five kinds of red mud under different pH conditions.The results show that under the three different pH ranges of 12.5<pH<13.5,6.5<pH<7.5,1.5<pH<2.5,Sc in red mud mainly exists in the form of hydroxide,Ga exists in the form of Ga(OH)₄^-under neutral to alkaline conditions,acidic condition exists in the form of Ga³⁺,V exists in the form of H₂V₂O₄²⁺,V²⁺and VO²⁺respectively under three kinds of pH conditions,Li and Rb exist in the form of stable Li⁺and Rb⁺.Mo exists in the form of insoluble molybdate CaMoO₄under alkaline condition and under neutral conditions,the main form of Mo is MoO₄^2-,while under acidic conditions,it is mainly in the form of MoO₃(H₂O)₃.From the above conclusions,it can be seen that Li,Rb,Sc,Y,La,Ce,V,Ga and Mo of rare metals in red mud show good leaching effects,but their leaching rates and leaching composition are easily affected by the pH conditions in the environment.The numerical simulation results have a certain reference value for the resource recovery of rare metals in red mud.