Challenging the “Crago” double float process II. Amine-fatty acid flotation of siliceous phosphates

In the conventional phosphate flotation (Crago) process, 30–40% by weight of the silica present in the feed are floated twice, first by fatty acid, and then by amine. The Crago process is therefore inefficient in terms of collector efficiency. Also, the phosphate mining industry is faced with higher fatty acid prices, lower feed grade, and stricter environmental regulations. For these reasons, the Florida Institute of Phosphate Research has developed an amine fatty acid flotation flowsheet, the reverse “Crago”. In this process, fine sands are first floated with a minimum dosage of amine condensate added stepwise. The concentrate from prefloat is then floated with a blend of surfactant/fatty acid/fuel oil. The technical and economic feasibility of this process were evaluated on seven feeds of varying characteristics, producing concentrates analyzing 30–32% P205 and 4–10% Insol with P205 recoveries of over 93%, at total reagent costs below $2 per ton of concentrate. This novel process could simplify the current processing fiowsheet by eliminating the acid scrubbing circuit, reducing the sizing section, and reducing the number of conditioners. The process consumes about one third to half the amount of reagents required by the Crago process at significantly improved flotation recovery. The effect of slimes (in either the flotation feed or water) and techniques for reducing this effect were also investigated.