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Carbonate ions (CO32–) play a vital role in CaCO3 scaling. The main goal of the present research was to study the inhibition of CaCO3 scaling during the vacuum evaporation salt-making process by regulating the doses of NaOH and Na2CO3 to promote the utilization efficiency and reaction activity of CO32–, and then to decrease the concentration of scale-forming ions, especially CO32–, in the refined brine obtained from purification via the NaOH-Na2CO3 method. The results demonstrate that the employed method not only achieved the improved efficiency of calcium (Ca2+) and magnesium (Mg2+) ion removal, but also effectively decreased the concentration of CO32– in the refined brine. The total concentration of Ca2+ and Mg2+ was decreased from 486.1 to 12.3 mg/L, and the concentration of residual CO32– during the brine purification process was 128 mg/L at the optimal doses of NaOH = 0.25 g/L and Na2CO3 = 1.3 g/L. The optimal parameters of the NaOH–Na2CO3 method were used in industrial production experiments and operated for a production period. The degree of accumulation of CO32– in the circulating feed brine was decreased, and the deposition ratio of CaCO3 was inhibited effectively. Additionally, the heat-transfer efficiency of the vacuum evaporation system was improved, and the energy consumption level was decreased. Moreover, large NaCl crystals with a narrow particle size distribution were prepared, thereby improving the anticaking property of the crystals. The scanning electron microscopy (SEM) results demonstrate that the surfaces of calcite CaCO3 were adsorbed by many spherical Mg(OH)2 particles, and the growth rate of calcite was retarded. Furthermore, the loose structure of the scale layer is beneficial to later cleaning treatment.

The “CO2–NaOH” brine purification method and flocculation performance of polyacrylamide (PAM) flocculants in vacuum salt making brine purification process are reported in this paper. The scale-forming trends of the brine were assessed by the Langlier index (LSI), the Ryznar stability index (RSI) and the Larson-Skold index (LR). The thermodynamic calculation results and PAM flocculant coagulation mechanism show that removal of Ca2+ and Mg2+ ions and suspended solids (SS) from brine by the “CO2–NaOH” method and PAM flocculants is feasible. The total concentration of Ca2+ and Mg2+ ions was decreased from 486.1 mg/L to 3.41 mg/L, and SS was decreased from 20 mg/L to 5 mg/L at the optimal experimental condition of CO2 flow velocity of 0.04 m3/h, injection time of 30 min, equilibrium pH of 11.5, and the dosage of the FL2949 and AN945SH PAM flocculants of 1 mg/L. LSI, RSI and LR show that the scale-forming was slowed down by brine purification. PAM flocculants were not retained in the brine as confirmed by the analysis of total organic carbon and chemical oxygen demand, and the X-ray diffraction, Fourier transform infrared, and scanning electron microscopy electron dispersive spectroscopy measurements for the flocs sludge during the brine purification process, results shown that the flocs sludge is calcite CaCO3. PAM flocculants purification was applied in industrial testing and achieved deep brine purification to remove scale-forming ions and SS. Additionally, it was found that the “CO2–NaOH” brine purification method promotes the utilization of CO2.

Solvent extraction and separation of indium and copper from zinc residue reductive leach liquor containing a high concentration of zinc (ca. 85 g/L) and iron (ca. 35 g/L) was studied. Di-(2-ethylhexyl) phosphoric acid (D2EHPA) and Acorga M5640 were used as extractants for indium and copper, respectively. Indium was preferentially extracted by 15%(v/v) D2EHPA with three-stage extraction using an aqueous/organic (A/O) phase ratio of 6/1. Indium was effectively stripped from the D2EHPA organic phase by 4 M HCl. Copper was subsequently extracted selectively from the indium-extracted solution using 15%(v/v) Acorga M5640 with three-stage extraction using an A/O phase ratio of 2/1. Copper in the loaded Acorga M5640 organic phase was stripped by a synthetic spent electrolyte solution containing 25 g/L Cu and 180 g/L H 2 SO 4 . Based on the experimental results, a flowsheet for the separation and recovery of indium and copper from the reductive leach solution was developed and tested. The results showed that 95.4% of indium and 95.5% of copper were extracted, and the measured separation factors β In/Zn , β In/Cu , β In/Fe , β CuZn , and β CuFe were 4979, 1975, 3719, 1719, and 2446, respectively.

Selective extraction of Mo by Cyanex-272 and tributyl phosphate (TBP) was investigated from the leach liquor of a low grade Ni–Mo ore, which contains mainly Mo(VI), Fe(III), Ni(II) and a small quantity of other impurities. The elements in the leach liquor were divided into four groups based on the extraction mechanism of acid phosphorus extractants, and the behavior of four elements (Mo, Fe, As and V) was investigated. The separation factors of Mo to Fe, As and V were calculated separately using di-2-ethylhexylphosphoric acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphine acid (Cyanex-272) under the same conditions. Cyanex-272 was found to be the optimum extractant. The synergistic coefficients of Cyanex-272 and co-solvents (secondary caprylic alcohol and TBP) were calculated separately for the extraction of Mo, Fe, As and V and TBP was found to be the better choice. Several operational factors such as initial leach liquor pH, extractant concentration, co-solvent concentration and stripping reagent concentration were examined to establish suitable conditions for the effective extraction and stripping of Mo. The separation factors, β Mo/Fe = 1803.61, β Mo/As = 480.09 and β Mo/V = 103.22, were obtained under the optimum experimental conditions of 15%(v/v) Cyanex-272, 15%(v/v) TBP, initial leach liquor pH of 0.0 and organic/aqueous (O/A) phase ratio of 1.0. The theoretical number of stages required for extraction and stripping was determined from the McCabe–Thiele diagrams. Molybdenum (11.62 g/L) was extracted in five stages with an O/A ratio of 1.0, yielding a raffinate with only 0.30 g/L Mo. Three stripping stages yielded a 98.0% Mo stripping efficiency from 11.23 g/L Mo loaded organic phase, producing an enriched 55.05 g/L Mo solution that contained 0.058 g/L As and 0.023 g/L V. A high purity final MoO 3 product (99%) was obtained by re-crystallization from the stripped Mo solution.