Abstract: The concentrated ash was taken as the research object, HCl was used as the acid washing leaching agent to elute heavy metals into the acid washing solution. The effects of three heavy metal precipitators of flake alkali (NaOH), 30% NaOH solution, and Na2CO3 powder on the precipitation and recovery of Zn, Pb, Cu, and Cd in the acid washing solution were studied. The results showed that at pH 7~9, there was an increasing trend with the increase of pH, and the precipitation removal efficiency of NaOH type precipitants for heavy metals was much higher than that of Na2CO3 type precipitants; when pH>9, the growth trend of its removal rate became slow or slightly decreased. Among them, when the pH of flake alkali (NaOH), 30% NaOH solution, and Na2CO3 powder were 9, 10 and 10, the removal efficiency of the four heavy metals reached the peak, which were 97.95%, 98.71% and 99.41%, respectively. The removal efficiency of heavy metals by the three types of precipitants was not significantly different, but considering the engineering application value of cost, transportation, storage, and feeding, as well as safety production, flake alkali (NaOH) was used as a heavy metal precipitant. When the pH value of the reaction solution was adjusted to 10, the removal effect of heavy metals in the concentrated lime acid washing solution was the best, which was the most suitable for engineering application.

Key words: concentrate ash, acid pickle, precipitant, heavy metal removal