Technique for reclaiming iron from waste slag in production of boric acid and magnesium sulphate by

This invention produces boric acid through collbranite in the following ways: grinding collbranite into 80-120 mesh; adding ore powder and saturated mother liquid boric acid in the autoclave with a solid and liquid rate of 1: 3-5; injecting sulfuric acid to make mother liquid sulfuric acid, with a density of 7-9 percent (wt); heating it to 70-90 C; reacting for 2-3h; filtering the reacted slurry; adding 85-95 C water and washing; cooling the filtered mother liquid and crystallizing then filtering; washing through saturated mother liquid and drying to obtain the boric acid; proceed with low-pressure evaporation and condensing for separated boric acid; cooling; crystallizing under normal temperature; washing through normal temperature saturated mother liquid; drying and obtaining boric acid. This method has small water consumption, low energy consumption, simple operation, not less than a 75 percent of B₂O₃ yield, and above 99.5 percent boracic acid in the product, and low production costs. It is particularly suitable for producing boracic acid from low-grade collbranite.