Pretreatment-Membrane Electrolysis Process for Treatment of Ammonium Sulfate Double Salt Crystals Formed During Electrolytic Manganese Production

Ammonium sulfate double salt crystals (ASDSCs) are a by-product formed during the electrolytic production of manganese. The long-term open-air stacking of ASDSCs leads to the manganese and ammonia nitrogen present inside leaching with rainwater, which seriously damages the ecological environment. To find a reasonable treatment method, we developed a pretreatment-membrane electrolysis method, which allowed for the recycling of ASDSCs stepwise. At the beginning, the ASDSCs were dissolved in water. The Mn2+ and Mg2+ present in the crystals were converted into MnCO3 and MgCO3 and recycled for the production of electrolytic manganese. The filtered liquid (mainly ammonium sulfate) was electrically decomposed to generate ammonia water and sulfuric acid, which were recycled for electrolytic manganese production. The results show that under the optimal conditions of a current density of 300 A/m2—an electrolysis time of 11 h and a temperature of 40 °C—the decomposition rate of ammonium sulfate reached 98.4%. This method led to the complete decomposition and utilization of the ASDSCs and truly achieved the green electrolytic production of manganese.