Simulated solution condition experiment and process design for copper deep removal from nickel anodes based on ion-exchange

Abstract

Removing copper from nickel electrolysis anode solution has been a major keypoint in the nickel metallurgy industry. In this study, we proposed a novel process flow to promote removing copper from nickel electrolysis anode solution. A simulated nickel anode solution was designed, and static and dynamic adsorption experiments were conducted to determine the best of solution pH, adsorption time and temperature, resin dosage and particle size, and stirring speed. The optimal conditions were explored for copper removal from nickel electrolysis anode solution. Based on the optimal experimental conditions and the relevant experimental data, a novel process for copper removal from nickel electrolysis anodes was designed and verified. This novel process of copper removal from nickel electrolysis anodes was confirmed with nickel anolyte solution with nickel 50−60 g/L and copper 0.5 g/L. After finishing the novel process of copper removal, the nickel in the purified nickel anolyte became undetectable and copper concentration was 3 mg/L, the novel process of resin adsorption to remove copper from nickel anode solution through static and dynamic adsorptions has an efficacious copper removal. It is a beneficial supplement to traditional methods.

1. Introduction

Removing copper from nickel electrolysis anode solution has been a challenge in the nickel metallurgy industry, which requires a copper concentration of less than 4.72×10⁻⁵ mol/L in the solution after copper removal, also the mass ratio of copper to nickel in copper slag needs to be greater than or equal to 15 [1−3]. In order to achieve this goal, a large number of metallurgical workers have conducted extensive long-term research work and proposed various methods for copper removal, including electrochemical method, chemical precipitation, solvent extraction, and ion exchange methods, but the drawbacks have not been overcome [4, 5]. Among them, electrochemical method can efficiently remove high content of copper in nickel anode solution, but it is not effective for trace amounts of copper. The mainstream method is chemical precipitation [6−8], but this method takes away a large amount of nickel during the removal of copper. Solvent extraction achieves a balance between the above two aspects [9], but due to the toxicity of solvents, they are not environmentally friendly.

Ion exchange resin is an artificially synthesized polymer material containing functional groups. The essence of ion exchange method is a reaction between exchangeable ions on the resin and metal ions in solution [10]. There are three main types of resins: anion exchange, cation exchange, and chelating resins [11]. Anion exchange resin forms complex anions with Cu²⁺ when Cl⁻ concentration of the solution is greater than 1.5 mol/L, while Ni²⁺ does not form anionic complexes when the concentration of Cl⁻ is between 0.1 and 12 mol/L [10, 12]. By adjusting the concentration of chloride ions, Cu²⁺ is separated from nickel anode solution using an anion exchange resin [13, 14]. However, this method requires a large amount of hydrochloric acid and has high recovery and separation costs, making it unsuitable for industrial production [15, 16]. Cation exchange resin is a type of resin that adsorbs metal ions in the form of ion bonds by functional groups in the resin [17]. The charge number of metal ions affects the adsorption force, and the formation of hydrated ions affects the adsorption distance [18]. The selectivity coefficient of cation exchange resin for heavy metal ions decreases with the increase of its hydration radius and charge number [19]. Therefore, cation exchange resin has a good separation effect on metal ions with high valence differences and small hydration radius, such as Cr³⁺ and Pb²⁺, but has weak selectivity for metal ions with the same valence state. Since Ni²⁺ and Cu²⁺ are both divalent and have no valence difference, cation exchange resins are usually not used for the separation of nickel and copper. Chelating resins can form stable complexes with heavy metal ions and are widely used in wastewater treatment [20]. Chelating resins have greater selectivity to nickel and copper, and their regeneration