Research by the Bureau of Mines includes efforts to devise means for maximum recovery of critical and strategic metals from primary and secondary domestic resources. As part of that effort, the Bureau developed a hydrometallurgical process to recover CO, ni, and cu from Missouri lead-smelter matte. The process includes leaching with h2so4 plus mNO2 as an oxidizing agent, liquor purification, selective precipitation of cus, (co,ni)s, and mnco3, and crystallization of na2so4. This report is concerned primarily with liquor purification, in which as and fe are removed from the leach liquor by ph adjustment and filtration. Two variations of the purification step are described. One variation provides liquor containing less than 1 mg/l as and fe but requires two solid-liquid separations. The other is achieved with only one solid-liquid separation but leads to a lower degree of purification.