Siliceous ores such as rhodonite, or slag such as that from a blast furnace producing ferromanganese, is melted with 1.6-6.6 Wt pct b2o3 or any boric acid or salt thereof in an amount providing that proportion of b2o3, at 1,350 deg.-1,450 Deg. C for a period required for a homogeneous melt, and cooled rapidly, as by quenching in water. The quenched material is ground wet, preferably to a slurry containing 10-30 pct solids, sized between 35 and 200 mesh, and leached with any strong mineral acid having ph approximately 2, the sulfate anolyte of an electrolysis cell being suitable, for generally 25-45 min. Certain dissolved impurities, including fe and a little si can be precipitated before filtering the slurry, by raising the ph to approximately 4 with powdered limestone or any convenient basic agent. When rhodonite ore containing 28.8 pct mn was crushed and blended with various amounts of b2o3 as na2b4o7, melted, quenched, and leached as 185-g batches each in 1.8 L of h2so4 at ph 2 for 1 h, then partially neutralized to ph 4 and filtered, the extraction of mn into solution was 95.8 pct in 25 min leaching when 1.6 pct of the melt was b2o3, 97.3 pct in 25 min with 3.5 pct b2o3 used, 98.4 pct in 30 min with 6.6 pct b2o3, and only 89.4 pct in 60 min with no b addition.
U.S. Pat. 3,575,697; Apr. 20, 1971; Chem. Abstr. 75:24,191N