| Abstract |
The report gives results of a preliminary process design and economic evaluation of a process for using lime/limestone scrubbing wastes as a source of calcium in the extraction of alumina (for use in aluminum production) from low grade domestic ores such as clays and coal ash. The other principal process feedstocks are soda ash and coal. The products are alumina, elemental sulfur, and dicalcium silicate, an alternate feedstock in the manufacture of portland cement. The conceptual plant is located next to a 1000 MW coal-burning power plant which generates > 1 million tons per year (tpy) of lime/limestone scrubber wastes. The required selling price for the alumina produced at 10% discounted cash flow would be $195-370 per ton, depending on the credit for sludge removal, exclusive of cement manufacture. If the alumina plant were co-located with an 860,000 tpy portland cement plant selling cement at $50 per ton, the required alumina selling price would be $27-221 per ton. Based on the current market price for alumina ($160 per ton), the portland cement plant appears to be necessary to make the process viable. In addition to the scrubber wastes, the process requires 12,000 tpy of soda ash, 300,000 tpy of clay, and 273,000 tpy of coal to produce 70,000 tpy of alumina, 156,000 tpy of sulfur, and 625,000 tpy of dicalcium silicate (used to produce 860,000 tpy of portland cement). |
