Basic Research On Gallium Enrichment And Recovery Of Other Valuable Elements From Yellow Phosphorus Electrostatic As

Gallium（Ga）is an important rare metal widely used in semiconductor manufacturing industry.With the rapid development of new energy,electronic communication,aerospace and other high-tech fields,the demand and use of Ga metal are also increasing.However,there are few independent deposits of Ga with industrial mining value in nature,and it is mainly recovered as a by-product from the production process of metals such as Al and Zn.As a result,the production of Ga is greatly limited,forcing people to find new Ga-containing resources and methods to recover Ga more efficiently.Yellow phosphorus flue dust is a solid waste produced during the production of yellow phosphorus by electric furnace method.It has attracted extensive attention of researchers because it is enriched with about 0.05%of Ga.At present,researchers mainly use the hydrometallurgical process to leach Ga from yellow phosphorus flue dust,but there are some problems such as complex process,large consumption of chemical reagents and liquid waste production.Based on this,this paper focuses on yellow phosphorus flue dust,and proposes a new process for enriching Ga and separating heavy metals such as Zn and Pb by vacuum carbothermal reduction method.At the same time,in view of the high phosphorus content in raw materials,the sodium carbonate roasting-water leaching process was used to remove and recover phosphorus,and finally a new technical process for comprehensive recovery of valuable elements from yellow phosphorusflue dust was proposed.The main research contents and conclusions are as follows:（1）The phase composition,chemical composition and element distribution of yellow phosphorus flue dust were studied by means of XRD,SEM-EDS,XRF and other modern analytic technology.The results show that the main phases of yellow phosphorus flue dust are KH₂PO₄,Ca₃（PO₄）₂and apatite minerals.Although the chemical composition of the raw material is complex,it is mainly composed of O,P,K,and Si,accounting for about 80%.Metal elements such as Zn,Pb,Al,and Ga are uniformly distributed in the raw materials,,among which Ga mainly exists in the form of oxides and the content is only 0.045%.（2）Based on the thermodynamic calculation results of Ga-C-O system,the volatilization and condensation mechanism of Ga and its oxides in the process of vacuum carbothermal reduction were clarified.First,the Gibbs free energies of the carbothermal reduction related reactions of Ga-oxide under normal pressure and 10 Pa pressure were calculated respectively to judge the order of the reactions.Then,the volatilization characteristics of gallium and its oxides at different temperatures were analyzed by the saturated vapor pressure,and the relationship of the components in the Ga-C-O system with temperature under normal pressure and 10 Pa was clarified.The thermodynamic calculation results indicated that the increase of reaction temperature and the decrease of system pressure are beneficial to the formation and volatilization of elemental gallium.In addition,the reduction of system pressure can reduce the Gibbs free energy of the reaction,which is conducive to the reduction of metal oxides and promote metal evaporation to the condensation zone.In the pressure of 10 Pa and the temperature range of 273 K-1473 K,the reduction reaction of Ga₂O₃will preferentially obtain Ga₂O,CO and Ga,in which Ga₂O volatilizes into the condensation zone and undergoes disproportionation reaction to generate Ga and Ga₂O₃,while most of Ga remains in the residue due to the low saturated vapor pressure and reacts with Ga₂O₃to obtain Ga₂O,and a small part of Ga volatilizes to the condensation zone for enrichment.（3）The accuracy of the thermodynamic calculation results was verified,and the optimal experimental parameters for Ga enrichment from yellow phosphorus flue dust were obtained.The vacuum carbothermal reduction experiment was carried out with99.99%purity Ga₂O₃under the conditions of 1273 K,10 Pa and 2 h.The experimental results showed that the products was mainly composed of elemental Ga in the region with higher condensation temperature,and the product was mainly composed of a mixture of Ga and Ga₂O₃in the region with lower condensation temperature.The phase of the residue was mainly composed of unreacted C and Ga₂O₃,but SEM-EDS analysis showed that a large number of micron-sized particles were attached to the surface,and these particles were mainly composed of Ga element.XPS analysis results showed the presence of Ga⁰in the residue,indicating the generation of Ga.This experimental phenomenon was consistent with the theoretical calculation results.The single factor experiments of yellow phosphorus flue dust showed that Ga volatilization rate reached about 92%under the optimal conditions of reaction temperature 1323 K,reducing agent dosage 50 wt%,holding time 60 min and pressure 1-10 Pa.Ga was highly enriched in the region with higher condensation temperature,gallium content reached 1.02%and impurity elements were less,which is about 20 times that of the raw material.The reduction reaction process is controlled by the interface chemical reaction,and the activation energy was 122.22 k J/mol.（4）The feasibility of separation of other valuable metals in yellow phosphorus flue dust was explored,and a new technical scheme of two-step vacuum carbothermal reduction for separation of Zn and Pb and enrichment of Ga was proposed.First,Zn and Pb were pre-separated under the experimental conditions of temperature 1173 K,reducing agent dosage 30%,holding time 60 min and 5-10 Pa.The volatilization rates of Zn and Pb reached 92.47%and 99.78%,respectively,while the loss rate of Ga was only 1.33%.The feasibility of enriching Ga from the residue obtained after separation of Zn and Pb was investigated.Under the conditions of temperature 1323 K,reductant dosage 40 wt%and 5-10 Pa for 60 min,the volatilization rate of Ga reached 87.57%and Ga content in Ga-rich condensate reached 1.37%,which was further enriched.（5）Phosphorus in yellow phosphorus flue dust was removed and recovered.Most of phosphorus-containing compounds in the raw material were converted into water-soluble Na₃PO₄by Na₂CO₃roasting process.Under optimum parameters of temperature 1173 K,Na₂CO₃addition 50 wt%,roasting time 100 min,water leaching temperature 313 K,liquid-solid ratio 13 m L/g,stirring time 45 min,and stirring speed600 r/min,The leaching rate of phosphorus reached 85.38%,while the content of Ga in the water leaching residue reached about 0.1%.Phosphorus in the aqueous solution was recovered by evaporation concentration and cooling crystallization.Phosphorus was mainly precipitated in the form of Na₂HPO₄,but the purity of the crystallization product needs to be further improved.（6）A new technical process of Na₂CO₃roasting-water leaching-two-step vacuum carbothermal reduction to enrich Ga and recover Zn,Pb and P from yellow phosphorus flue dust.The condensed products with Pb content of 80.56%,Zn content of 98.57%and Ga content of 1.49%and crude Na₂HPO₄were obtained,respectively.In summary,the technical process proposed in this paper has the advantages of simple process,no use of strong acid or strong alkali.It has potential promotion and application value,and provides a theoretical and experimental basis for the high-value utilization of yellow phosphorus flue dust.