Recovering Value from End-of-Life Batteries by Integrating Froth Flotation and Pyrometallurgical Copper-Slag Cleaning

In this study, industrial lithium-ion battery (LIB) waste was treated by a froth flotation process, which allowed selective separation of electrode particles from metallic-rich fractions containing Cu and Al. In the flotation experiments, recovery rates of ~80 and 98.8% for the cathode active elements (Co, Ni, Mn) and graphite were achieved, respectively. The recovered metals from the flotation fraction were subsequently used in high-temperature Cu-slag reduction. In this manner, the possibility of using metallothermic reduction for Cu-slag reduction using Al-wires from LIB waste as the main reductant was studied. The behavior of valuable (Cu, Ni, Co, Li) and hazardous metals (Zn, As, Sb, Pb), as a function of time as well as the influence of Cu-slag-to-spent battery (SB) ratio, were investigated. The results showcase a suitable process to recover copper from spent batteries and industrial Cu-slag. Cu-concentration decreased to approximately 0.3 wt.% after 60 min reduction time in all samples where Cu/Al-rich LIB waste fraction was added. It was also showed that aluminothermic reduction is effective for removing hazardous metals from the slag. The proposed process is also capable of recovering Cu, Co, and Ni from both Cu-slag and LIB waste, resulting in a secondary Cu slag that can be used in various applications.

Element Distribution and Migration Behavior in the Copper Slag Reduction and Separation Process

Copper slag is a solid pollutant with high recyclability. Reduction and separation are regarded as effective disposal methods. However, during the melting process, the separation and migration behavior of elements in the copper slag is complicated. Thus, the formation of pollutants cannot be controlled merely by optimizing the operation parameters. The elemental distribution and migration behavior are discussed in this work. In reduction experiments, the copper slag smelting liquid was divided into three layers: a reduction slag layer, a reactive boundary layer, and an iron ingot layer. Reduction slag and ingot iron were on the top and bottom of the liquid, respectively. Residual carbon oozed at the interface. C can react with reducible “O” atoms, which exist in 2FeO·SiO2, Fe3O4, and CuO. Meanwhile, CO was generated and overflowed from the liquid layer. After reduction by C or CO, metallic iron and copper were produced and migrated to the iron ingot layer. In the liquid, S gradually diffused into the upper layer. Some of the ZnO and CuS spilled from the liquid into the flume. After reduction, CaO·SiO2 was generated and moved to the upper layer.

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

The Fe3O4 and Fe2SiO4 in copper slag were successfully reduced to metallic iron by coal-based direct reduction. Under the best reduction conditions of 1300 °C reduction temperature, 30 min reduction time, 35 wt.% coal dosage, and 20 wt.% CaO dosage (0.75 binary basicity), the Fe grade of obtained iron concentration achieved 91.55%, and the Fe recovery was 98.13%. The kinetic studies on reduction indicated that the reduction of copper slag was controlled by the interfacial reaction and carbon gasification at 1050 °C. When at a higher reduction temperature, the copper slag reduction was controlled by the diffusion of the gas. The integral kinetics model research illustrated that the reaction activation energy increased as the reduction of copper slag proceeded. The early reduction of Fe3O4 needed a low reaction activation energy. The subsequent reduction of Fe2SiO4 needed higher reaction activation energy compared with that of Fe3O4 reduction.

Mechanism of oxides reduction during bubbling of copper-smelting slags by CO–CO2 gas mixtures

The paper suggests a mechanism of simultaneous oxide reduction from multicomponent copper-smelting slags during their bubbling with CO–CO2 reducing mixtures and provides a numerical algorithm developed to implement this mechanism as a mathematical model. The first feature of the suggested mechanism is a statement that the total speed of the overall reduction process is determined by CO consumption during its interaction with oxygen ions formed in slag oxide dissociation. The second feature is a statement about equilibrium achieved between slag, alloy and gaseous phase according to the system oxidizing potential reached at every instant. The paper demonstrates a satisfactory agreement between calculated and experimental data obtained when reducing industrial coppersmelting slags at 1300 °С and СО/СО2 = 4, 6, 156, and using the first-degree kinetic equation regarding the difference between initial and equilibrium CO contents in the gaseous phase. A generalized kinetic constant of the multicomponent slag reduction reaction rate is calculated as k = 2.6·10–7, moles CO /(cm2 · sec·%) at 1300 °С. It is shown that during industrial multicomponent slag reduction, reduction speed of copper (I) oxide and magnetite are high and close to maximal ones as early as at the first minutes of slag bubbling with reducing gas. At the same time, for Fe(II), lead and zinc oxides they are low at the first minutes of the process, and increase gradually to reach their maximum, and then decrease again up to near-zero values as the supplied gas and melt come to equilibrium. Generally, oxide reduction speed naturally decreases with approaching to equilibrium between the initial gas and liquid phases, and this should be taken into account when designing continuous slag depletion processes.