Hoechst Aktiengesellschaft

Johannes Scheffer

Gunther R Schimmel

Friedrich Kolkmann

A process is provided for working up dusts which have been precipitated electrostatically from the gas mixture composed essentially of carbon monoxide and phosphorus vapor produced in the electrothermal production of yellow phosphorus, which process comprises converting the dusts into a calcinate at 300.degree. to 800.degree. C. under oxidizing conditions in a first step, leaching the calcinate with phosphoric acid in a second step, adjusting the pH of the solution in phosphoric acid to 0 to 1.5 with sodium hydroxide solution in a third step, precipitating the sulfides of lead, copper and cadmium from the partially neutralized solution in phosphoric acid by adding sulfide and filtering them off in a fourth step, adjusting the pH of the filtered, partially neutralized solution in phosphoric acid to about 1.5 to 5.0 with sodium hydroxide solution and precipitating zinc sulfide, if necessary by adding further quantities of sulfide, and filtering it off in a fifth step, further neutralizing the sodium phosphate solution, if necessary after expelling excess sulfide, with sodium hydroxide solution and separating it from precipitated calcium compounds in a sixth step, and using the resultant sodium phosphate solution in this form in a known manner to produce sodium phosphate salts.

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Vlissingen, Netherlands

Johannes Scheffer