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Removal of MgO from Phosphate Pebble by Flotation: Phase II



Phosphate rock as it is mined in Florida contains an increasing quantity of magnesium. The magnesium is present as discrete particles of dolomite (calcium magnesium carbonate). High magnesium adversely affects both the production of phosphoric acid (lowers phosphate recovery or production rate) and acts as a diluent in the final fertilizer products. Therefore, this study was initiated to investigate a novel reactive flotation (RF) technology to separate dolomite from dolomitic phosphate ores. Research results suggested that polyvinyl alcohol (PVA) could be used to coat phosphate rock containing a high concentration of magnesium. This coated rock was then placed in a 3% sulfuric acid solution where CO2 was generated on the surface of the dolomite. The bubbles of gas remained attached to the dolomite and floated it to the surface. Typically the remaining rock contained over 90%of the phosphate and had an MgO concentration of less than 1%. Spray coating gave PVA consumptions as low as 1 pound per ton.

Several separation techniques were tested and a sluice like device was found to give the best separation results. The chemical consumption cost was estimated to be less than $2.15 per ton of feed with an electrical cost of less than $1.00 per ton of feed. Other operating costs, including depreciation, should add no more than $2.50 per ton of feed. With typically over 70% of the feed tons being recovered as product, this represents a product rock cost of $8.10/ton. This is comparable to current typical flotation costs (to recover less than 1 mm size phosphate particles) of >$10.00/ton of product. Nevertheless, more work is still needed to optimize this separation process and to further evaluate its economics.