Influence Of Coexting Ions In The Leaching Solution Of Coal Gasification Slag On The Adsorption Of Lithium And Gallium

Lithium and gallium are important strategic resources.With the dramatically increasing market demand for lithium and gallium,the extraction from secondary resources,such as coal gasification slag,has become a hot spot in current research.Generally,lithium and gallium need to be transferred from solid phase to the liquid phase by leaching for extraction,and then they are further separated and enriched.The alkaline leaching solution of coal gasification slag contains complex components and low concentration of lithium and gallium.The sorption method exhibits many advantages such as high recovery and strong selectivity,and it is especially suitable for separating lithium or gallium with a low concentration.However,it is still unclear about the effect of impurity ions on the sorption of lithium and gallium.Therefore,Si O₃^2-,Al（OH）₄^-and Ca²⁺were selected as impurity ions because of the high concentrations in the leaching solution of coal gasification slag,and the influences of them on the sorption of lithium and gallium were investigated.The experiments were carried out firstly in the simulated solution prepared using pure reagents,and then research results were verified in the actual leaching solution of coal gasification slag.In this study,HMn₂O₄（HMO-1）,H_1.33Mn_1.67O₄（HMO-2）and H_1.6Mn_1.6O₄（HMO-3）were selected as sorbents for Li⁺,and the resins called ACD-800,LSC-600 and D887were used for Ga（OH）₄^-sorption.The proerties of sorbents were characterized by scanning electron microscopy and automated specific surface area analyzers.The results showed that HMO-1 possessed a morphology of octahedron with obvious cracks,while HMO-2 and HMO-3 presented cubic and sphere-like particles,respectively.The specific surface areas of HMO-1,HMO-2 and HMO-3 are 32.6,97.4 and 5.9 m²/g,respectively.The resins named ACD-800,LSC-600 and D887 are spherical particles with pores on their surfaces,and their specific surface areas are 25.3,14.8 and 9.1 m²/g,respectively.In addition,the sorption experiments were carried out in order to analyze the sorption performances of sorbents.The results showed that the sorption of Li⁺by HMO can reach equilibrium within 12 h,and their sorption capacities of Li⁺increased with the increase of solution p H.At the initial p H of 12,the sorption capacities of Li⁺by HMO-1,HMO-2 and HMO-3 are 19.58,30.35 and 32.74 mg/g,respectively.For sorption of Ga,the sorption equilibriums of Ga（OH）₄^-by ACD-800 and LSC-600 can be achieved with 4 h,while D887 only needs 2 h.The sorption capacities of Ga by resins decreased firstly and then increased with the increase of solution p H,and their sorption amounts of Ga are 2.96,5.14 and 2.84 mg/g at the initial p H of 12,respectively.The influences of Si O₃^2-,Al（OH）₄^-and Ca²⁺on the sorption of Li⁺were investigated.Under the single impurity ion system,Si O₃^2-and Al（OH）₄^-suppressed the sorption of Li⁺by HMO-1,HMO-2 and HMO-3.When the concentration of Si is 4000 mg/L,the sorption capacities of Li⁺by HMO decreased to 15.14,25.29 and 28.25 mg/g,respectively,while the sorption capacities of Li⁺in the presence of Si with 4000 mg/L decreased to 4.96,8.33 and 9.63 mg/g,respectively.However,Ca²⁺only inhibited the sorption of Li⁺by HMO-2 and HMO-3,and had almost no effect on HMO-1.The sorption capacities of Li⁺by HMO droped to 20.39,23.10 and 26.87 mg/g in the solution containing Ca of 4000 g/L,respectively.The sorption of Li⁺by HMO was suppressed in the coexistence system of Si O₃^2-and Al（OH）₄^-and the coexistence system of Si O₃^2-,Al（OH）₄^-and Ca²⁺.Mn²⁺released during the sorption process can react with Si O₃^2-to generate Mn Si O₃ precipitation,leading to the decrease of Mn content in HMO.Thus,the sorption capacities of Li⁺by HMO through the redox pathway decreased.Al（OH）₄^-was converted to Al（OH）₃ during the sorption process,which can cover the surfaces of sorbents,hindering the mass tranfer of Li⁺and Mn²⁺between the solution and the sorbents.Ca²⁺can be attached to the surfaces of HMO,making it difficult to adsorb Li⁺due to charge mutual repulsion.As for the sorption of Ga by resins,the sorption capacities of Ga by ACD-800,LSC-600 and D887 in the solution with 20 mg/L Ga are 2.49,2.27 and 2.36 mg/g,respectively.Compared to sorption of Ga under the above conditions,Si O₃^2-,Al（OH）₄^-and Ca²⁺in the single impurity ion system promoted the sorption of Ga（OH）₄^-by resins,and the coexistence of Si O₃^2-and Al（OH）₄^-and the coexistence of Si O₃^2-,Al（OH）₄^-and Ca²⁺were beneficial for the sorption of Ga（OH）₄^-.The sorption capacities of Ga by ACD-800,LSC-600 and D887 in the presence of 4000mg/L Si increased to 2.96,2.82 and 4.08 mg/g,and the sorption amounts in the solution with Al of 4000 mg/L increased to 3.72,3.81 and 4.03 mg/g,respectively.When the concentration of Ca is 4000 mg/L,the Ga sorption amounts were increased to 7.68,7.63and 7.39 mg/g.Si O₃^2-,Al（OH）₄^-and Ca²⁺can break the resin surfaces and enlarge the pore size,which is benefical for the bingding between Ga（OH）₄^-and the functional groups（=NOH）of resins.Besides,there is no competition between Ca²⁺and Ga（OH）₄^-because of their different binding modes with resins.Instead,there is an electrostatic attraction between Ca²⁺adsorbed on the resins and Ga（OH）₄^-,which promotes the sorption of Ga（OH）₄^-.The sorption performances of HMO and resins in actual leaching solution of coal gasification slag and simulated solution were investigated.The p H and the concentrations of Li and Ga of simulated solution is the same as that of actual leaching solution.When the amount of HMO is 0.025 g/L,the recovery rates of Li⁺by HMO-1,HMO-2 and HMO-3 in simulated solution were 60.87%,64.77%and 55.60%,respectively,whereas their recovery rates in the leaching solution decreased to 26.62%,52.41%and 55.60%.When the amount of the resin is 1 g/L,the recovery rates of Ga（OH）₄^-by ACD-800,LSC-600 and D887 in simulated solution were 21.90%,33.61%and 46.08%,respectively,whereas their recovery rates in the leaching solution increased to 56.21%,58.84%and 82.38%,which are consistent with the results of the previous study.The distribution coefficient and selectivity coefficient were used to determine the sorption selectivity of the sorbent for Li⁺and Ga（OH）₄^-in the actual leaching solution.HMO shows high selectivity of Li⁺in the actual leaching solution,while it is difficult for resins to separate Ca²⁺and Ga（OH）₄^-.The thesis contains 64 figures,12 tables,and 103 references.