Recovery of Iron from Copper Slag Using Coal-Based Direct Reduction: Reduction Characteristics and Kinetics

Determining the Reactivity of Selected Biomass Types Considering Their Application in Pyrometallurgical Processes of Metal Production

In this paper, results of research on the reactivities of selected biomass types considering their application in pyrometallurgical processes of metal production are presented. Walnut shells, sunflower husk pellets and spent coffee grounds were selected as biomass materials. Their use as potential reducers in the process of metallurgical slag decopperisation is an innovative approach to this subject. The thermogravimetric findings show that all three tested biomass types are classified as highly reactive. The time to reach maximum reactivity ranges from 1.5 to 3 min and, the lowest value is recorded for the sample of spent coffee grounds. The sample hold time of two hours enables copper content reduction to approx. 1 wt% for practically all the reducers tested. A longer duration of liquid slag contact with the reducer results in a decreased copper content in the slag to a value below 1 wt%. Copper concentrations of 0.5 wt% and lower are observed with a hold time of 4 h. The preliminary results indicate that there is great potential for the use of this type of material in non-ferrous metallurgy, which may translate into replacing fossil raw materials and thus introducing the principles of a sustainable process in this case of metal production.

Reduction Kinetics of Copper Slag by H2

In order to maximize the utilization value of copper slag, a process of smelting copper–iron alloy with copper slag is proposed here. The reduction kinetics of copper slag by H2 are studied in this paper. The main phases of the copper slag were Fe2SiO4 and Fe3O4. The suitable conditions of reduction were a temperature of 1373.15 K, a H2 partial pressure of 40%, and a calcium oxide addition amount of 30%. In these conditions, the metal reduction ratio was 85.12%. The copper slag, after reduction, was heated to 1773.15 K for 4 h. The content of iron in the metal was 85.11%, and the copper content was 10.40%. According to the unreacted nuclear model, the reduction process of copper slag is controlled by internal diffusion and chemical reaction. With the increase of the reduction ratio, internal diffusion is the main influencing factor. The activation energy of H2 reduction copper slag is 29.107~36.082 kJ/mol, which decreases gradually with the H2 partial pressure’s increase. The metal obtained by copper slag reduction contains a certain amount of sulfur, and a desulfurization process is required before it is used.

Environmental and Socioeconomic Impact of Copper Slag—A Review

Copper slag is generated when copper and nickel ores are recovered from their parent ores using a pyrometallurgical process, and these ores usually contain other elements which include iron, cobalt, silica, and alumina. Slag is a major problem in the metallurgical industries as it is dumped into heaps which have accumulated into millions of tons over the years. Moreover, they pose a danger to the environment as they occupy vacant land (space problems). Over the past few years, studies have been conducted to investigate the copper slag-producing outlets to learn their behavior, as well as properties of slag, to have the knowledge of how to better reuse and recycle copper slag. This review article provides the environmental and socioeconomic impacts of slag, as well as a characterization of copper slag, with the aim of reusing and recycling the slag to benefit the environment and economy. Recycling methods are considered an attractive technological pathway for reducing waste and greenhouse gas emissions, as well as promoting the concept of circular economy through the utilization of waste. These metal elements have value depending on their characteristics; hence, copper slag is considered as a secondary source of valuable metals. Some of the pyrometallurgical and hydrometallurgical processes to consider are physical separation, magnetic separation, flotation, leaching, and direct reduction roasting of iron (DRI). Some of the possible metals that can be recovered from the copper slag include Cu, Fe, Ni, Co, and Ag (precious metals).