中国有色冶金

To address issues such as high impurity content, limited reusability, and environmental hazards in molten salt chloride residues from titanium metallurgy processes, a high-temperature stratified treatment process using sodium sulphate has been proposed. This process generates insoluble sulphates through the reaction of sodium sulphate with calcium and magnesium ions in the residues, subsequently employing stratified deposition to separate and recover the upper and middle layers of molten salt. Thermodynamic studies indicate that solidification reactions proceed spontaneously within the 400~1200℃ temperature range, though the reaction driving force diminishes with increasing temperature. When temperatures fall below below 800℃, both Kp(MgSO₄) and Kp(CaSO₄) are less than 2.01×10^-3; conversely, when temperatures exceed 800℃, Kp(MgSO₄) progressively surpasses Kp(CaSO₄) due to competitive effects between Mg²⁺ and Ca²⁺ ions. Consequently, the optimal reaction temperature should be maintained between 800 and 950℃. Experimental results indicate that under optimised conditions of 900℃ reaction temperature and a molar ratio of sodium sulphate to impurities of 1∶1, the process treatment achieves optimal performance. Calcium removal rates in the upper and middle molten salt layers reached 69% and 88% respectively, while magnesium removal rates attained 93% and 89% respectively, satisfying the 60% calcium-magnesium removal standard for re-melting. Microstructural analysis of the lower layer sample via SEM-EDS confirmed that impurity elements predominantly precipitated as stable, insoluble compounds such as MgSO₄, CaMgSiO4, and CaMg₃(SO₄)₄. This process not only achieves efficient separation of impurity elements from waste slag but also offers significant advantages including straightforward operation and low running costs. It provides a practical technical solution for the resource recovery of titanium metallurgical waste slag, holding considerable industrial application value and environmental significance.