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The sulfide precipitation has been widely used to recover Cu(II) and remove As(V) in copper smelting electrolyte based on the Cu(II)-As(V) separation. However, the recovery efficiency was undesirable due to the inaccurate control of process parameters. It was necessary to investigate the process and mechanisms of sulfurization precipitation for accurate adjustment. Herein, under the single and mixed solutions of Cu(II) and As(V), the process parameters were investigated and the precipitation mechanisms were explored. And when using actual electrolytes, the corresponding sulfurization process and mechanisms were also revealed. The sulfurization results of single component solutions suggested that Cu(II) was rapidly precipitated in one step, but As(V) firstly generated intermediate, then it was gradually reduced to As(III) for a longer time and quickly precipitated in the form of amorphous. This phenomenon caused the significantly faster removal speed of Cu(II) than that of As(V). For their mixed solutions, only a small amount of As(V) were removed by adsorbing the precipitate at the low S/Cu molar ratios (R S/Cu), and Cu(II) and As(V) could achieve a good separation. Simultaneously, it revealed that the sulfidation competitive mechanisms were related to the solubility product constant (Ksp) and initial As(V) concentrations. In addition, the similar rules were also observed in actual electrolytes. Moreover, under R S/Cu = 1.2 and reaction time of 10 min, the arsenic content of sulfide precipitates in the actual electrolyte was less than 2.5%, which showed a great separation also could be obtained for the actual electrolyte. This result met the requirement of Cu(II) recovery. It can provide a good reference for adjusting sulfidation parameters in the actual process to achieve efficient copper recovery, reduce the production of hazardous waste containing arsenic at the source and realize the cleaner production of copper smelting system. [Display omitted] • The removal speed of As(V) was greatly slower than that of Cu(II) in sulfidation. • The conversion of H 3 AsO 3 S was influenced by the R S/As and reaction temperature. • The Cu(II)-As(V) separation mechanism in sulfurization was revealed. • The Cu(II)-As(V) competitive mechanism in sulfidation was revealed. • As Content in CuS slag obtained in actual copper electrolyte was less than 2.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • UV high-reference differential absorption spectrometry alleviated linear deviation. • The upper limit for As(III) direct detection could be as high as 20.00 g/L. • TD-DFT results showed that redshift was related to electron transition variation. • P within 98 %-104 % and RSD of < 1.50 % indicated good accuracy and precision. • The proposed method was faster, cheaper and more eco-friendly than common methods. The current methods for determining high-concentration As(III) in the high-acid matrix from the copper smelting industry are complex, time-consuming, and costly. This limits effective modulation of sulfurizing agent dosage for As(III) removal via sulfurization, aggravating hazardous waste generation. Herein, a simple, rapid, and nondestructive UV high-reference differential absorption spectroscopy was developed to directly determine high-concentration As(III) in simulated high-acid wastewater. Time-dependent density functional theory calculations indicated that the spectral curve redshift with As(III) concentration increasing was related to the decrease of electron transition energies and energy gaps. When using high-reference solutions, the least redshift in the maximum absorption wavelength and the highest upper limit of linear fitting concentration could be obtained. Therefore, the piecewise quantitative linear model of differential absorbance and concentration was established under high-reference. The quantitative range of the model within 0.06–20.00 g/L As(III) with a mean relative error of < 5.0 % and standard recovery rates within 98.0 %-104.0 % indicated high accuracy. Additionally, the relative standard deviations of < 1.5 % (n = 5) revealed good precision. All results indicated the high feasibility of the developed method in alleviating linear deviation caused by redshift and absorption saturation. Furthermore, it has potential significance in saving sulfurizing agent dosage and reducing hazardous waste generation from the source, thereby facilitating a cleaner process for removing As(III) via sulfurization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The precipitation difficulty of HMI sulfide is co-determined by Ksp value, H+ concentration and S(-II) concentration. • The positive-side and negative-side competitive sulfuration behaviors of concomitant HMIs on Cu(II) recovery are exhibited. • The S(-II)-combining process on HMIs surface is divided into S(-II)-capturing and S(-II)-consuming stages. • The Cu(II) quantitative model is established to provide instantaneous concentration for solving Cu(II) recovery issues. Currently, sulfuration is widely used for the Cu(II) recovery from copper smelting waste acids (CSWA). However, the abundant concomitant heavy metal ions (HMIs) seriously obstruct Cu(II) recovery. In this paper, we find that the precipitation difficulty of HMI sulfide is determined by solubility product constant (Ksp), H+ concentration and S(−II) concentration, resulting in the diversified competitive sulfuration behaviors of concomitant HMIs on Cu(II) recovery. For concomitant HMIs without S(−II)-consuming ability, the positive-side competitive sulfuration behaviors on Cu(II) recovery are in the order of In(III) > Zn(II) > Ni(II) > Fe(II) > Mn(II). However, with the formation of concomitant HMIs sulfides, the negative-side competitive sulfuration behaviors on Cu(II) recovery are in the order of Fe(III) > As(III) > Bi(III) > Cd(II). According to the results of diffusion-growth-dissolution model, the S(−II)-combining process on HMIs surface is divided into S(−II)-capturing and S(−II)-consuming stages, related to Ksp value and HMIs precipitation, respectively. In actual CSWA, 5000 ∼ 15000 mg/L As(III) seriously inhibits the recovery efficiency of 500 ∼ 2000 mg/L Cu(II), and other concomitant HMIs (e.g., 250 ∼ 1200 mg/L Zn(II), 300 ∼ 450 mg/L Cd(II), 10 ∼ 200 mg/L Bi(III) and 20 ∼ 200 mg/L Fe(II)) will further affect Cu(II) recovery. Besides, ignoring these diversified competitive sulfurations of concomitant HMIs induces unreasonable S(−II) concentration for complete Cu(II) recovery, resulting in Cu(II) recovery issues: As(III) precipitation and Cu(II) residue. Thus, timely information in instantaneous Cu(II) concentration is a feasible strategy to accurately adjust S(−II) concentration via Cu(II) quantitative model. This work is devoted to the efficient and controllable recovery of Cu resources and the reduction of As-containing hazardous wastes in sulfuration treatment of actual CSWA. [ABSTRACT FROM AUTHOR]

Currently, domestic and foreign copper smelting waste acid mainly employ sulfuration method to realize the separation of Cu(Ⅱ) and As(Ⅲ), facing the problem of unreasonable sulfidizing agent dosage and sulfidation time. If excessive sulfidizing agent dosage or overly long sulfidation time, it will lead to human health threat and large hazardous waste volume. If insufficient sulfidizing agent dosage or overly short sulfidation time, it will cause the waste of copper resources and substandard treatment solution. In this paper, the competitive sulfuration mechanism of Cu(Ⅱ)/As(Ⅲ) solution (C (As(Ⅲ)) = 10 g/L) with different Cu(Ⅱ) concentrations is revealed, i.e., when C (Cu(Ⅱ)) ≥7 g/L, the sulfidation sequence of Cu(Ⅱ) and As(Ⅲ) follows the solubility product constant (Ksp); when C (Cu(Ⅱ)) ≤6 g/L, the precipitation process of Cu(Ⅱ)/As(Ⅲ) is dominated by the liquid-phase mass-transfer mechanism (ion diffusion). The sulfide precipitation of Cu(Ⅱ)/As(Ⅲ) is a co-deposition process. With the increase of sulfidizing agent dosage (S/Cu ratio) and sulfidation time (t), the Cu(Ⅱ) concentration gradually decreases to reach complete removal, while the further increase of S/Cu ratio and t leads to the decrease of copper content in the sulfide precipitates. Finally, the methods are demonstrated that detected accurately Cu(Ⅱ) and As(Ⅲ) concentrations in a rapid and non-destructive manner. This work not only provides a novel perspective on the efficient separation of Cu(Ⅱ)/As(Ⅲ) in copper smelting waste acid, but also opens a unique approach for direct and rapid detection of Cu(Ⅱ)/As(Ⅲ) concentration during the sulfuration process. Hence, this research is a guide for the regulating means (S/Cu and t) in the actual multi-step sulfuration process of copper smelting waste acid treatment and electrorefining solution purification. [Display omitted] • The sulfuration of Cu(Ⅱ)/As(Ⅲ) solution is a co-deposition process. • The competitive sulfuration reaction between Cu(Ⅱ) and As(Ⅲ) for S2- will occur. • Influences on copper content of sulfide precipitates: sulfidizing agent dosage (S/Cu ratio) and sulfiding time (t). • The rapid, non-destructive and accurate quantitative analysis methods of Cu(Ⅱ) and As(Ⅲ) are demonstrated. [ABSTRACT FROM AUTHOR]