The Bureau of Mines evaluated a sulfurous acid-sulfuric acid process for recovering alumina from clay, in which clay is leached successively with sulfurous acid and sulfuric acid. The resulting aluminum sulfite and aluminum sulfate solutions are combined and heated to produce a basic aluminum sulfate and sulfur dioxide. Alumina is extracted from the basic aluminum sulfate as sodium aluminate by leaching with dilute sodium hydroxide. After desilication, sulfuric acid is used to precipitate alumina as alumina trihydrate, which is then calcined to alpha-alumina. The estimated fixed capital cost for a plant producing 1,000 tons per day of alumina is about $74 million on a 1971 basis. For comparison with previous alumina-from-clay evalulations, the estimated fixed capital cost for the plant is about $67 million on an m and s chemical equipment index basis of 240.0, Which is equivalent to a 1960 cost level. Because the operating cost is highly dependent on fuel and electric power costs, graphs are included to show the effect of these items on the operating cost. On a 1971 basis, with natural gas costing 35 cents per million btu and operating labor costing $4 per hour, the estimated operating cost is about $100 per ton of alumina. On a 1960 basis, with labor costing $2.30 Per hour and natural gas costing 25 cents per million btu, the estimated operating cost is about $86 per ton of alumina.