Development of recovery technology of valuable metal contained in industrial sludge by smelting reduction furnace with two-stage tuyeres

A new technology for recycling stainless pickling sludge has been developed by combination of a smelting reduction process of the sludge and a separation process of fluorine from the pickling. The stainless pickling sludge, which is generated by the neutralization of the waste pickling liquor, contains valuable metals such as iron, chromium and nickel. The sludge, however, also contains fluorine and the fact has obstructed the recycle of the sludge. We carried out bench-scale and pilot plant tests of the smelting reduction with coke packed bed in order to develop the recovery technology of valuable metal contained in the sludge. The reduction of the metal hydroxides and the behavior of the fluorine in the furnace were studied through the tests. A newly modified index of heat level was installed. By considering decomposition heat of hydroxide and reaction heat with carbon, reduction indices were uniformly described. Complete recovery of the valuable metals in the sludge was achieved at the pilot plant tests. The fluorine distribution ratio into slag was 21% and we expect that the fluorine leaching from the slag is 0.32 mg/l, which is lower than the environmental standard value of 0.8 mg/l. The pH of the cooling water for the off gas is mainly determined by the balance of the ion contents of fluorine and chlorine as the acid elements and that of calcium, sodium and potassium as the alkali elements.