Study On Synergistic Treatment And High Value Utilization Of Coal Fly Ash And Spent Pot-lining

The safe treatment and high-value utilization of coal fly ash（CFA）and spent pot-lining（SPL）are still major issues in the world today.At present,the contradiction between the supply and demand of aluminum resources in China is serious.The content of alumina in solid waste CFA and hazardous waste SPL is high,which can be used as an important potential resource for alumina production.In this paper,a new method of synergistic treatment and extraction of alumina from fly ash and waste channel liners is proposed,which is of great significance to reduce land occupation,reduce environmental load and guarantee the sustainable development of China’s aluminum industry.The process scheme combining sintering activation and hydrochloric acid leaching was used to treat CFA and SPL innocuously and resourcefully.The physical and chemical properties of CFA and SPL were systematically investigated by modern analysis and testing technologies such as XRF,XRD,SEM,FTIR,and TG-DSC.The reaction principle of sinteri ng activation and hydrochloric acid leaching was proved by metallurgical thermodynamic analysis,single factor,and orthogonal experimental methods were used to optimize the process of synergistic extraction of alumina from CFA and SPL.The main research contents and conclusions are as follows:（1）The alumina content of CFA and SPL in the experiment was40.02%and 29.70%,respectively,with alumina extraction potential.It is difficult to leach alumina directly because part of the alumina in CFA is wrapped in a glassy body with an inactive Al₂O₃-Si O₂ network structure.However,SPL can be used as an activator to react with CFA to generate soluble aluminum salts when co-heated and sintered with CFA.Accordingly,the process flow for the synergistic treatment of fly ash and waste tank liners was initially determined as follows:physicochemical property analysis,sintering activation,hydrochloric acid leaching,solid-liquid separation,concentration,and crystallization,and high-temperature calcination.（2）The negative values of Gibbs free energy change（（35）_r G_m）of the main chemical reactions of CFA and SPL during sintering activation and hydrochloric acid leaching are large,indicating that the reaction has a larger thrust,and the high temperature is more conducive to the activation reaction.The reaction principle of sintering activation and hydrochloric acid leaching process was determined:Na F in SPL and Na₂CO₃ generated from Na₂O in the sintering process can decompose with the aluminum-containing minerals mullite and silica in CFA,respectively.Moreover,the activation reaction of Na₂CO₃ with CFA has more competitive advantages than Na F.The cyanide in SPL can be harmlessly treated by oxidative decomposition through high-temperature sintering.The aluminum-containing sintering products are converted into aluminum ions in the acid leaching solution by acid leaching.（3）The experimental optimization study of CFA activation and alumina extraction process was carried out by single factor and orthogonal experimental methods,and the optimum experimental conditions of the sintering process were obtained as follows:material ratio(m _CFA/m _SPL)1:0.7,sintering temperature 800℃,sintering time110min;the optimum experimental conditions of acid leaching process were:liquid-solid ratio 20:1,hydrochloric acid concentr ation 6mol/L,acid leaching temperature 100℃,acid leaching time 120min,and the dissolution rate of Al₂O₃ can reach 92.36%.（4）The structure of the metallurgical grade alumina product prepared in the experiment is a mixed crystal form ofθ-Al₂O₃ andα-Al₂O₃.After CFA and SPL mixture are treated under optimized conditions,the soluble F^-and CN^-concentrations in the leaching solution of fluoride and cyanide are lower than the allowable emission concentration limits stipulated by the state.