Innovative Methodology for Sulfur Release from Copper Tailings by the Oxidation Roasting Process

Abstract

To effectively prevent the accumulation of copper tailings from producing acid mine drainage (AMD) and maximize the comprehensive utilization of copper tailings, the process of oxidation roasting was adopted to release sulfur in the form of SO2 to achieve the purpose of sulfur recovery later. Based on the AMD risk assessment, thermogravimetric (TG) analysis, and differential scanning calorimeter (DSC) analysis, the influences of roasting temperature, residence time, and air flow in the roasting process were investigated. The thermal stability, reaction equilibrium, mineral transformation, and residual S content were characterized by TG-DSC, HSC chemical software 6.0, X-ray diffraction (XRD), and combustion neutralization, respectively. The optimum conditions for sulfur release in the roasting process were shown with a temperature of 1200°C, a residence time of 60 min, and an air flow of 0.8 L/min. Under these conditions, the sulfur release rate was 99.82%, and the residual S content was 0.05%. Subsequently, the process of sulfur release was proposed as four steps: oxidative decomposition of pyrrhotite, formation of ferric sulfate, decomposition of ferric sulfate, and formation of hematite. All of the findings could propose a theoretical and experimental reference for the recovery of the sulfur component from tailings rich in sulfide minerals.

Recovery of γ-Fe2O3 from copper ore tailings by magnetization roasting and magnetic separation

“…Sulfur compounds were easy to decompose and release sulfur with the increasing roasting temperature ranging from 1,000 to 1,350°C [19]. After roasting at 1,200°C with the duration time from 20 to 60 min, the sulfur release rate reached to 99.78% and the residual S content reduced to 0.06% [4]. In this study, roasting temperature was set as 1,000, 1,050, 1,100, 1,150, and 1,200°C, and roasted time was 10 min, with the airflow of 5 L min −1 .…”

“…Owing to the characteristics of pyrrhotite with more sulfur and less iron, the purpose of magnetization roasting was to release sulfur first [4] and then to oxidize magnetite to maghemite. The possible reactions during magnetization roasting were expressed as follows:…”

“…Copper ore tailings contain pyrrhotite (Fe (1-x) S, where 0 ≤ x < 0.223), which has three homogeneous polychromatic variants of iron sulfide mineral and tends to produce acid mine drainage because of oxidation [2,3]. To effectively prevent the environmental risk of the copper ore tailings and recycle the sulfur resource in the copper ore tailings, the sulfur released as SO 2 can be collected to produce sulfuric acid by oxidation roasting as mentioned in the previous study [4]. Meanwhile, the iron units are concentrated in the roasted slag and existed in the form of γ-Fe 2 O 3 .…”

“…Therefore, sulfur release was studied first in previous study [4]. In this paper, the magnetizing roasting of the copper ore tailings followed by magnetic separation is further investigated to recover γ-Fe 2 O 3 from the roasted slag.…”

“…, the content of Fe 2 O 3 reached 36.35 wt%. When the copper ore tailings were roasted from 600 to 1,200°C, the roasted slag was magnetic which contained γ-Fe 2 O 3[4]. Therefore, it was necessary and meaningful to roast to release sulfur first and recycle γ-Fe 2 O 3 subsequently.…”