CHALLENGING THE CRAGO DOUBLE FLOAT PROCESS .2. AMINE-FATTY ACID FLOTATION OF SILICEOUS PHOSPHATES

In the conventional phosphate flotation (Crago) process, 30-40% by wei ght of the silica present in the feed are floated twice, first by fatt y 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 o f Phosphate Research has developed and amine-fatty acid floatation flo wsheet, the reverse ''Crago''. In this process, fine sands are first f loated with a minimum dosage of amine condensate added stepwise. The c oncentrate from prefloat is then floated with a blend of surfactant/fa tty acid/fuel oil. The technical and economic feasibility of this proc ess were evaluated on seven feeds of varying characteristics, producin g concentrates analyzing 30-32% P2O5 and 4-10% Insol with P2O5 recover ies of over 93%, at total reagent costs below $2 per ton of concentrat e. This novel process could simplify the current processing flowsheet by eliminating the acid scrubbing circuit, reducing the sizing section , and the reducing the number of conditioners. The process consumes ab out one third to half the amount of reagents required by the Crago pro cess at significantly improved flotation recovery. The effect of slime s (in either the flotation feed of water) and techniques for reducing this effect were also investigated. (C) 1997 Elsevier Science Ltd.