Phosphoric acid manufacturing with converted waters

Modified wet-process manufacturing of phosphoric acid, wherein phosphate rock is reacted with sulfuric acid in a reactor and wherein by-product gypsum filter cake is washed repeatedly then is slurried and finally is stacked to drain, comprising

• forming separate process waters containing contaminants by condensing steam and other gases from wet-process flash coolers and evaporators, and by scrubbing wet-process vent gases;
• recovering P.sub.2 O.sub.5 from process leaks, spills, and washes with one of the process waters, clarifying it, returning the underflow to the reactor, and preliminarily washing the gypsum filter cake with the clarified water;
• and
• raising the pH of the other process water, in a first stage toward neutral and in a second stage beyond neutral, clarifying it, removing precipitated contaminants in the underflows from both stages, re-acidifying the clarified water to nearly neutral pH about 6 to 7, and washing the wet-process by-product gypsum filter cake with the clarified re-acidified water.

Method of producing by-product gypsum collected as filter cake, slurried, and stacked to drain in wet-process phosphoric acid manufacturing, substantially free of contaminants, comprising

• treating process water contaminated with dissolved fluorine, heavy metals, and radioactive compositions as well as residual P.sub.2 O.sub.5,
• in a first stage of partial neutralization and clarification, including removing underflow containing, those of said precipitated contaminants insoluble at the pH to which partially neutralized, and
• in a second stage of alkalization and clarification, including removing underflow containing, remaining said precipitated contaminants soluble at the pH to which partially neutralized but insoluble at the pH to which alkalized, and
• in a stage of re-acidifying to nearly neutral pH about 6 to 7, producing a slightly acidic, non-scaling, pH-adjusted water (pH-AW).

Wet-process phosphoric manufacturing process modified by producing a decontaminated water as follows:

• treating gypsum stack water obtained from filter cake water by partially neutralizing it with limestone to a pH of about 4.5 and clarifying it,
• then alkalizing the partially neutralized clarified water with lime to a pH of about 11 and clarifying it, and
• acidifying the alkalized clarified water to a pH of about 6 to 7, to yield a non-scaling pH-adjusted water and using the resulting pH-adjusted water in the wet-process in at least two of the following ways:
• scrubbing wet-process vent gases,
• condensing steam from wet-process flash coolers & evaporators,
• washing wet-process by-product gypsum filter cake, as make-up water added where needed in the wet-process.