Nucleation crystallization pelleting process for highly efficient manganese ion recovery in electrolytic manganese wastewater

To address the issues of wasting manganese resources and generating hazardous chemical sludge during the removal of manganese (Mn) ions from acidic electrolytic manganese wastewater using conventional chemical precipitation, an innovative nucleation crystallization pelleting process (NCP) was proposed. The NCP aimed to recover Mn ions without generating hazardous sludge. By pre-adding seeds with active sites for Mn ions attachment into the NCP reactor, Mn ions were induced to adhere to the seed surfaces in the form of MnCO3 by adjusting the Na2CO3 dosage and hydraulic conditions. The results demonstrated effective Mn ion removal, with Mn ions being reduced from 3800 mg/L to about 20 mg/L after five-stage NCP reactors. The Na2CO3 dosage for the first to fifth stage was 3.0, 2.6, 2.2, 1.65, and 1.2 g/L, respectively. Optimizing the hydraulic conditions facilitated enhanced mass transfer between Mn ions and seeds, with the optimum upward flow rate of the reactor determined as 60 m/h. In addition, the optimized seed filling ratio was found to be 15 %. The seeds exhibited stability as they were recycled three times, and the crystallization of Mn ions showed little variation. Moreover, after a 20-day operation, the crystal seeds reached a size of approximately 0.8 mm, exhibiting a moisture content below 3 %. The grade of manganese ions exceeded 44 %, in terms of ore, and the extraction rate of manganese ions reached 98.17 % after acid leaching of the crystals. These crystals can be directly reused in the electrolytic manganese production, thereby improving the utilization rate of manganese ions. In conclusion, the NCP technology shows promise for effective Mn ion removal and recover without generating hazardous sludge.