A Study on Reduction of Copper Smelting Slag by Carbon for Recycling into Metal Values and Cement Raw Material

Urtnasan Erdenebold,Jei-Pil Wang

doi:10.3390/su12041421

Abstract

Copper smelting slag is a solution of molten oxides created during the copper smelting and refining process, and about 1.5 million tons of copper slag are generated annually in Korea. The oxides in copper smelting slag include ferrous (FeO), ferric oxide (Fe2O3), silica (SiO2 from flux), alumina (AI2O3), calcia (CaO) and magnesia (MgO). The main oxides in copper slag, which are iron oxide and silica, exist in the form of fayalite (2FeO·SiO2). Since copper smelting slag contains high content of iron, and copper and zinc, common applications of copper smelting slag can be used in value-added products such as abrasive tools, roofing granules, road-base construction, railroad ballast, fine aggregate in concrete, etc. Some studies have attempted to recover metal values from copper slag. This research was intended to recover ferrous alloy contained Cu, a raw material of zinc, from copper slag, and produce reformed slag such as blast furnace slag for Portland cement. As a result, it was confirmed that with reduction smelting by carbon at temperatures above 1400 °C, it is possible to recover pig iron containing copper from copper smelting slag, and the addition of CaO in reduction smelting helped to reduce iron oxide in the fayalite and change the chemical and mineralogical composition of the slag. The copper oxide in the slag can be easily reduced and dissolved in the molten pig iron, and zinc oxide is also reduced to a volatile zinc, which is removed from the furnace as fumes, by carbon during the reduction process. When CaO addition is above 5%, acid slag is completely transformed into calcium silicate slag and is observed to be like blast furnace slag.

Highlights

Since the beginning of the Industrial Revolution, byproducts such as the metallurgical slag left over when metals are produced from natural and secondary raw materials have been considered waste
The reduction smelting experiments on the recovery of iron from copper slag were performed by reduction agent carbon at high temperatures under holding temperature and holding time factors
In the reduction smelting process of copper slag, iron oxide might be reduced from the decomposition of fayalite by direct reduction with solid carbon and indirect reduction with CO gas following this reaction: Fe2SiO4 + CO = 2Fe + SiO2 + CO2 (1)

Summary

Introduction

Since the beginning of the Industrial Revolution, byproducts such as the metallurgical slag left over when metals are produced from natural and secondary raw materials have been considered waste. Dumping or disposal of copper slag causes wastage of metal values and leads to environmental problems. South Korea has a small land area and a high population. South Korea refuses to landfill metallurgical slags and promotes zero waste with the reuse and recycling of these waste materials. The potential uses of copper slag are a partial substitute in cement and aggregate in concrete [7,8]. These methods cannot efficiently recover a high content of iron and valuable metal in copper smelting slag

Methods

Results

Conclusion