Verminderung des Cadmium‐Gehaltes von Rohphosphaten und Mineraldüngern

Abstract

Reducing the cadmium content of crude phosphates and mineral fertilizers. Crude sedimentary phosphates generally contain cadmium together with traces of other heavy metals. These Cd traces generally end up in fertilizers produced from the crude phosphates. Processes have therefore been developed to separate the Cd from the crude phosphate or from the crude phosphoric acids arising therefrom as intermediates. In this way, the Cd content of the crude phosphate can be reduced to less the 10% of its original value, and to 50% thereof by extractive treatment with acidic calcium nitrate solution. Older calcination processes for crude phosphate have been improved to give residual Cd contents of 10 to 50% at temperatures of 800 to 1000°C. Cadmium can be removed almost quantitatively from crude phosphate by means of dialkyl dithiophosphoric acid esters by extraction, binding to adsorbents, or ion flotation. Cadmium can be extracted from crude acids in high yield by long‐chained amines. After partial neutralization of the crude acids, precipitation as cadmium sulphide is also possible.

The effect of thermal treatment on the properties of some natural phosphates

“…It has been shown [1] that the heating of natural phosphates is a promising procedure for the removal of detrimental impurities. During the preliminary thermal and mechanical treatment, some of the properties, the structure and the phase composition are changed.…”