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.

Abstract: A method for production of sulfur dioxide from calcium sulfate by high temperature thermal reduction. Calcium sulfate, preferably in the form of calcined phosphogypsum, is desulfurized using a fossil fuel as a heat source, the combustion products resulting therefrom being used as a reductant. The fuel and reductant may be coal, coke, liquid hydrocarbons or natural gas; high sulfur, medium or low rank coal is preferred. The fuel is combusted with air or oxygen-enriched air. The solid feeds are introduced as finely-divided particles entrained in reactant gases, and the temperature is sufficiently hot to cause residual processed materials to melt and drain from the reaction vessel in the form of a liquid slag, yet not hot enough to produce significant amounts of fine silicon oxide dust. Iron pyrite, sand and/or clay can be added to reduce the slag melting point and to control its viscosity.