Research on nickel soot desalination by washing

Nickel soot is the soot collected from the tail gas during the nickel high-temperature smelting process, which is rich in heavy metals such as lead and soluble salts such as sodium. The complex composition of nickel soot and the high salt content constrain its resource utilization. How to efficiently separate soluble salts is the technical key to nickel soot resource recovery. Taking the smelting soot of Gansu Jinchuan Nickel Sulfide Mine（the main phases of which are PbSO₄, Na₂S₂O₈, CdSO₄, etc., which are in the form of dense agglomeration） as the research object, it systematically investigates the effects of liquid-solid ratio, time and temperature on the elution rate of soluble salts in the process of single-stage washing, and finds that, in the process of single-stage washing when the liquid-solid ratio is 20 mL/g, and the washing is carried out in water under 25 ℃ for 15 min, the elution rates of Na, K, Cd, and Zn reach 85.39%, 56.77%, 51.21%, and 37.17%, respectively; while the elution rate of Pb is extremely low（＜0.14%）, and that of Ni, Fe, Al, and Cu are 22.73%, 3.85%, 17.73%, and 22.56%, respectively; the ash quality decreases due to the dissolution of the salts after the aqueous washing, and the Pb content is elevated from 20.70% to 37.63% （about 2-fold enrichment）, and insoluble metal fractions such as Fe, Cu, Sn, Si, Bi, and Ca are elevated from 9.87%, 2.58%, 4.49%, 3.65%, 2.23%, and 3.57% to 16.00%, 3.44%, 5.21%, 5.88%, 2.92%, and 3.87%, respectively. The results of the study reveal the high water consumption of the single-stage washing process. Based on this, a three-stage counter-flow washing process for nickel soot is proposed, which simultaneously achieves efficient elution of soluble salts, enrichment of metallic lead, and recycling of water resources through a graded cycle operation. The results show that when the liquid-solid ratio of the three-stage counter-flow washing is reduced to 3 mL/g, the elution rate of Na and Cd is still maintained at ＞80%, and the elution rates of Zn and K are 65.80% and 42.41%. Physical and morphological analyses show that washing mainly dissolves soluble sodium and cadmium salts leading to an increase in amorphous state, but do not change the crystal structure and agglomerate morphology; Pb and other metal elements are enriched while Na and Cd decrease. This study shows that washing can efficiently synergise desalination and heavy metal enrichment, and the constructs three-stage counter-flow washing process significantly improves the elution rate of Na and Cd, significantly reduces the water consumption of the elution process （85% water saving compared with the single-stage）, and provides technological support for the pre-treatment of nickel fume ash resource utilization.