As part of a continuing effort to develop technology that maximizes mineral and metal recovery from domestic resources, the Bureau of Mines investigated a method to totally utilize copper converter slags without recycling them back through the matte smelting furnace. The research was directed toward (1) recovering the contained copper in converting slags by producing a recyclable copper-iron matte, (2) carbothermically reducing the slags to recover the iron, and (3) producing slag wool from the depleted slags. This report deals with the reduction of three industrial converting slags, containing 2.0 to 7.3 wt-pct cu, in an 800-kva electric arc furnace to produce a recyclable copper-iron matte. The addition of sufficient iron pyrite to provide 29 to 113 pct of the stoichiometric sulfur (based on producing 40-pct-cu matte) produced a recyclable matte (36 to 61 pct cu) at an energy consumption of 520 to 700 kwh per ton of solid material charged. The expected energy saving for treating molten slag is an electric furnace (5- to 9-mva range) is about 400 kwh per ton of molten slag treated.