Abstract: Process for dissolving unwanted magnesium from phosphate ores by leaching with dilute sulfuric acid at automatically controlled pH. Minerals so treated are more easily converted by the conventional "wet" process into phosphoric acid, and yield better quality phosphoric acid. Magnesium So leached is precipitated with lime or dolime in a second conventional processing step to make byproduct magnesium hydroxide. An anion such as nitrate, acetate or formate is maintained in the recirculating leach solution in concentration sufficient that calcium sulfate does not precipitate with product magnesium hydroxide. Nearly pure carbon dioxide can be recovered as a second byproduct.