Synergistic Extraction System Research Articles

Recovery of valuable metals from manganese purification sludge (SPS) containing Mn-Ni-Co sulfide and preparation of battery-grade Ni-Co-Mn sulfate solution

The manganese production industry produces a large amount of sulfide purification sludge (SPS) every year, representing a hazardous solid waste but also a valuable secondary resource for Ni, Co, and Mn. In this paper, the recovery of Ni, Co, and Mn from the SPS was achieved by (i) leaching with a solution of hydrogen peroxide, (ii) selectively extracting nickel, cobalt and manganese, (iii) solvent extraction for zinc removal, and finally obtained the battery-grade Ni-Co-Mn sulfate solution. During the hydrogen peroxide solution leaching stage, the leaching efficiency of Co, Mn, and Ni reached 98.5%, 98.6%, and 95.6%, respectively. A synergistic extraction system (SES) consisting of decyl 4-picolinate and dinonylnaphthalene sulfonic acid was used to selectively extract Ni, Co, and part of Mn, and the extraction of Ni and Co was >99.8% and 95.5%, respectively. The loaded organic was subjected to four-stage countercurrent scrubbing using a 5 g/L H2SO4 solution, resulting in nearly 100% removal of Ca and Mg. After that, 150 g/L H2SO4 was used to strip Ni, Co, and Mn from the loaded organic to obtain a crude Ni-Co-Mn sulfate solution. Finally, D2EHPA was utilized for the extraction of impurity Zn from the stripping solution to obtain a battery-grade Ni-Co-Mn sulfate solution with <5 × 10−4 g/L of Zn. Compared to traditional technology, the novel process not only enables the recovery of valuable Ni, Co, and Mn in SPS but also facilitates their direct preparation into battery-grade nickel‑cobalt‑manganese sulfate solution, which has the advantages of a short process and high added value.

Selective extraction of nickel from acid leach solution of spent lithium-ion batteries using synergistic solvent extraction system consisting of TFCA-4PC

Selective extraction of nickel from acid leach solution of spent lithium-ion batteries using synergistic solvent extraction system consisting of TFCA-4PC

Separation of trace amount of nickel from cobalt sulphate solutions using a synergistic solvent extraction system consisting of dinonylnaphthalene sulfonic acid (DNNSA) and decyl 4-picolinate (4PC)

The current methods for separation of nickel from cobalt sulphate solutions have drawbacks of long flowsheets, release of large volumes of wastewater and incomplete separation of two metals. A synergistic solvent extraction (SSX) system consisting of dinonylnaphthalene sulfonic acid (DNNSA) and decyl 4-picolinate (4PC) is proposed in this work to extract nickel from cobalt sulphate solutions selectively. The extraction of nickel reached 99.7% after five-stage counter current extraction with an A/O volume ratio of 1/6 at 30 °C, resulting in a large increase of Co/Ni mass ratio to 25,700 in raffinate from 56 in feed. The loaded organic phase can be easily stripped using a dilute H2SO4 solution. Application of this process in industry is expected to make an important impact on the production of high-purity cobalt sulphate solutions and to deliver economic benefits.

Selective recovery of lithium from high-aluminum fly ash by using alkali-dissolution-assisted HBTA–TOPO synergistic extraction

The process of recycling lithium (Li) from common coal fly ash using strong acids can release substantial quantities of hazardous low-value residues, and the complex ionic composition of the acidic leaching solution hinders the selective extraction of Li. Accordingly, a green and economical approach was developed for the selective recovery of Li and extraction of valuable Al-rich residues from high-alumina fly ash (HAFA). In HAFA, the glass phase (the main Li-bearing phase) can be selectively dissolved in the mild NaOH solution at 95 °C for 2 h, and valuable mullite phase (the main Al-bearing phase) was retained in the leaching residue (Al2O3 content 49.00 wt%). The leaching efficiencies of Li, Si, and Al were 91.60%, 43.19%, and 3.56%, respectively. Among the primary metallic elements present in HAFA, only Li, Na, K, and Al in the glass phase were readily dissolved in the alkaline solution. Meanwhile, the synergistic extraction system of HBTA and TOPO has good complexing ability with Li + compared to Al3+, K+, and Na+. Therefore, Li+ can be selectively extracted from alkaline leaching solutions using HBTA and TOPO. The Li extraction efficiency reached 99.68% after three consecutive extractions under the optimal conditions. Finally, the used alkali leaching solution and synergistic extractants can be regenerated via Ca(OH)2 precipitation and HCl reverse extraction. These findings can provide new strategies for the green and overall utilization of HAFA.

Synergistic extraction of valuable metals from cyanide tailings slurry electrolyte and preparation of ferrous oxalate

A cyanide tailings slurry electrolyte (CTSE) was treated using a synergistic extraction system (P204-T) composed of di(2-ethylhexyl)phosphate (P204, (C8H17O)2PO2H, H2A2), trioctylamine (TOA, ([CH3(CH2)7]3N), R3N), and iso-alkanes, and a collaborative extraction technique involving oxalic acid stripping and photocatalysis was developed to separate and recover valuable metals and prepare ferrous oxalate. The results show that at a pH of 1.5, the P204 concentration of 15 vol%, TOA concentration of 10 vol%, O/A of 1:1, an oscillation time of 10 min, and an oscillation frequency of 190 rpm, the single-stage Fe(III) and Zn(II) extraction efficiencies of P204-T were 99.25% and 99.02%, respectively, and the saturated extraction capacities were 25.01 g•L−1 and 1.20 g•L−1, respectively. TOA destroyed the dimer structure of P204 and promoted the –OH bond and –OP group in P204 to combine with TOA through hydrogen bonding to form N–H+···O–P and N–H+···OP bonds, resulting in the R3NHA·(HA) composite structure. During the collaborative extraction process, ion exchange with FeSO4+ resulted in the formation of FeSO4A·(HA)3 and ion exchange with the intermediate product (R3NH)2SO4 and Zn(SO4)22- formed (R3NH)2Zn(SO4)2, which improves the extraction efficiency of metal ions. In addition, some amount of P204 underwent ion exchange with free Fe3+ and Zn2+ to produce FeA3(HA)3 and ZnA2(HA)2, respectively. At oxalic acid concentration of 1 mol•L−1, an O/A of 1:3, the efficiencies of Fe(III) and Zn(II) stripped from the saturated organic phase reached 99.65% and 99.41%. Zn(II) formed the ZnC2O4·2 H2O precipitate and Fe(III) separation. FeC2O4·2 H2O was successfully synthesized by ultraviolet photocatalysis using iron oxalate complex as the stock solution.

P350-N235 synergistic extraction system used for the recovery of Nd(III) from waste NdFeB magnets

The recovery of Nd(III) from NdFeB permanent magnets is gaining increasing attention. In the rare earth elements separation industry, wastewater produced through saponification has become a serious environmental problem. In this work, a novel non-saponification P350-N235 synergistic extraction system was established for the extraction of Nd(III) from nitric acid medium. Almost 100% of Nd(III) was extracted by using a P350-N235 system when the molar fraction (X) of P350 was 0.3. And the synergistic enhancement factor Rmax reached 60.03. Firstly, the effects of time, pH, volume ratio and other variables were investigated to determine the extraction behaviors. Response surface methodology (RSM) was used to optimize the extraction conditions. The mechanism of synergistic extraction was investigated by FT-IR, UV–vis, NMR methods and ESP maps, indicating that the composition of the extracted complex was Nd(NO3)3·(P350)2.5(N235)2.5. Then, the extraction thermodynamics and kinetics were also thoroughly investigated, the extraction process is demonstrated to be a spontaneously exothermic reaction. In the NdFeB leaching solution, the synergistic system showed excellent separation factor (β) for Nd/Sm (1.43), Nd/Gd (7.33), and Nd/Dy (9.81). Finally, after 5 cycles, the P350-N235 synergistic system maintained high extraction efficiency. In conclusion, this study overcame the saponification problem in traditional extraction techniques and proposed an environmentally friendly green extraction system.

Synergistic extraction and separation of thorium from rare earths in chloride media using mixture of Cextrant 230 and Cyanex 923

In order to lower the usage of expensive Cyanex 923 and increase the extraction capacity of the system of Cextrant 230, the synergistic extraction of thorium from chloride media by a mixture of Cextrant 230 and Cyanex 923 was investigated. The maximum synergistic enhancement coefficient (R) of 1.53 is obtained at 1:1 molar ratio of Cextrant 230/ Cyanex 923. The synergistic extracted species of Th4+ is determined as ThCl4·2Cextrant 230·Cyanex 923. The synergistic extraction of Th4+ is an entropy-driven exothermic process. The loading capacity of 0.60 mol/L mixed extractant for thorium is about 17.10 g/L (calculated as ThO2), and the loaded thorium in the organic phase can be effectively stripped by distilled water. For comparison, rare earth cations are barely extracted under the similar conditions, suggesting that the mixtures can be applied to separate thorium from rare earths. A cascade extraction process was developed based on the synergistic extraction system to separate thorium from the hydrochloric acid leaching of bastnaesite. The content of thorium in the leaching solution decreases obviously from 19.90 mg/L to 1.4 μg/L by 3 stages of extraction, which is superior to sole Cextrant 230 or Cyanex 923. The introduction of Cextrant 230 into the extraction system not only lowers the usage of Cyanex 923 but also enhances the selective extraction of thorium at low acidity, implying that the synergistic extraction system can selectively extract thorium more efficiently and economically than the sole systems.

A leaching, solvent extraction, stripping, precipitation and calcination process for the recovery of MoO3 and NiO from spent hydrofining catalysts

Effective recovery of elements from spent catalysts can not only avoid environmental hazards, but also alleviate the pressure of resource scarcity. This study proposes a hydrometallurgical process for the selective recovery of MoO3 and NiO from the spent hydrofining catalysts. First, valuable metals were leached with 0.5 mol/L H2SO4 and 4 wt% H2O2 at 25 °C for 20 min, resulting in the dissolution efficiencies of Mo, Ni and Al were 95.6%, 96.5% and 13.8%, respectively. Then, bis-(2-ethylhexy)phosphinic acid (P227) was chosen as the Mo extractant due to its higher separation factors of βMo/Al and βMo/Fe compared to di-2-ethylhexylphosphoric acid (P204) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). Extraction efficiency of 99.9% Mo was achieved at pH of 0.5 with 0.3 mol/L P227, whereas only 0.061 g/L Fe and <1 mg/L of other impurity elements were co-extracted. The complete stripping of Mo was realized with 0.4 mol/L (NH4)2CO3. Subsequently, a synergistic extraction system bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) and trioctylphosphine oxide (TOPO) was employed to extract Ni, where the extraction efficiency was more than 99.9%. Around 99.9% of Ni was stripped with 9 mol/L HCl. With the addition of TOPO, not only the extraction ability of Ni was improved, but also realized the complete stripping of Ni. The two oxides MoO3 and NiO were prepared from the stripping solution. In addition, the extraction mechanism of Mo and Ni was studied. The total recovery efficiencies of Mo and Ni were 94.1% and 93.1%, with the purity of 99.9% and 99.0%, indicating that this innovative process can be utilized to recover MoO3 and NiO from the spent hydrofining catalysts.

Direct Extraction of Ni(II) from Acidic Polymetallic Sulfate Media with a Novel Synergistic Extraction System of DNNSA-MSL211

Direct extraction of Ni(II) from Fe(III), Al(III), Ca(II), Mg(II), and Mn(II) is a bottleneck issue in the hydrometallurgy processes of laterite-nickel ore, spent batteries, and other secondary sources. One of the biggest challenges in achieving direct extraction of Ni(II) is the lack of stable and efficient extractants. Hence, a novel bipyridine extractant MSL211 was designed and synthesized in this paper. With its strong steric resistance and electrostatic interaction, MSL211 can form a stable eight-membered chelating ring with Ni(II), thereby having a high bonding ability toward Ni(II). Therefore, based on the high bonding ability of MSL211 toward Ni(II) and the low extraction capacity of DNNSA for Fe(III), an efficient synergistic extraction system of DNNSA-MSL211 was proposed. The synergistic extraction system of DNNSA-MSL211 realizes direct extraction of Ni(II) from Fe(III), Al(III), Ca(II), Mg(II), and Mn(II) without neutralization, precipitation, and solid/liquid separation processes, which are inevitable but problematic processes in the current hydrometallurgy processes for removing Fe(III), Al(III), and Mn(II). The effects of the molar ratios of DNNSA:MSL211, shaking time, temperature, O/A ratios, and equilibrium pH on the extraction behavior of Ni(II) were investigated. Under optimum conditions, the extraction efficiency of Ni(II) was as high as 97.62%, and the separation coefficient of Ni(II) over all impurities was greater than 400. To elucidate the mechanism of the high selectivity of DNNSA-MSL211 toward Ni(II), DFT calculations were carried out to calculate the binding energy (ΔE) and Gibbs free energy (ΔG(ext)) of the extraction process. Furthermore, this paper investigated the entire ″extraction-stripping″ process, demonstrating that the synergistic extraction system of DNNSA-MSL211 avoids neutralization, precipitation, and solid/liquid separation processes, minimizes hazardous waste generation, and shortens process flow while meeting the objectives of sustainable and clean production.

A new process to produce battery grade lithium carbonate from salt lake brines by purification, synergistic solvent extraction and carbon dioxide stripping

There are abundant lithium resources in China, and the demand for lithium salts is high. However, lithium resources of the sulfate salt lakes in Tibet, such as Baqiancuo Salt Lake, have not been effectively utilised. This study proposes a synergistic extraction system composed of LIX 54, TRPO, and surfactant ADD-1 for efficient lithium extraction from the brine and separation of impurities. The CO2 gas stripped lithium and produced high-purity lithium bicarbonate solution. Thermal decomposition produced lithium carbonate solid from the loaded strip solution. The comprehensive yield of lithium was higher than 95%, and the quality of the lithium carbonate product reached the battery chemical grade standard. This new process offers a new way for the utilisation of lithium resources in salt lakes.

Separation of rare earths in chloride media by synergistic solvent extraction with mixture of HEHAMP and CA12 and stripping with HCl

The synergistic extraction of rare earths (REs) from chloride media by a mixture of two extractants 2-ethylhexylaminomethyl phosphonic acid mono-2-ethylhexyl ester (HEHAMP, HA) and sec-octylphenoxy acetic acid (CA12, HB) was investigated. A remarkable positive synergistic effect was observed at the molar ratio of HEHAMP to CA12 being of 2:3. The extraction of REs was found to be a cation exchange process and the extracted species of Yb3+ was determined as YbCl2HAB. The separation factors (SF) of adjacent heavy REs, i.e. SFYb/Tm and SFLu/Yb, for the mixtures were 2.50 and 1.63, which were much higher than those of the sole HEHAMP and the sole CA12 system. In additional, the values of SFYb/Y and SFLu/Y were 7.17 and 11.14, respectively, which were higher than those of other reported synergistic systems and those of the sole HEHAEP or CA12 system, suggesting that the mixture of HEHAMP and CA12 is a potential synergistic extraction system for the separation of heavy REs and/or Y(III) from other heavy REs. A cascade extraction process for the separation of Y(III) from yttrium-enriched REs feed using the synergistic extraction system was developed, which are superior to sole CA12 system. The Y2O3 product with a purity of 99.4% was obtained by 8 extraction stages and 5 scrubbing stages.

Recovery of lithium from high Mg/Li ratio salt-lake brines using ion-exchange with NaNTf2 and TBP

In view of the complex problems for the ionic liquids (ILs) recovery with the system containing ILs and TBP, this work proposed a NaNTf2-based synergistic extraction system, NaNTf2 + TBP, which could realize the effective reutilization of the extraction system without reducing the lithium separation ability. Under the optimal extraction parameters, the extraction efficiency of Li+ exceeded 98%, while that of Mg2+ was only ~1%. The results of mass spectrometry (ESI-MS) and slope analysis showed that two TBP molecules involved in the extraction process of Li+, and the Li+ extraction mechanism obeyed the cation-exchange process. According to the red shift of the FT − IR peak of PO in TBP and the chemical shift changes of P in 31P NMR, the interaction strength between TBP and different metal ion followed the sequence: ETBP−H >> ETBP−Li > ETBP−Mg > ETBP−K > ETBP−Na. It was also found that after a three−stage countercurrent extraction process, [Li+]org was 0.42 g L−1, and the total recovery efficiency of Li+ was about 98%. The saturated extraction capacity for Li+ could be as high as 5.4 g L−1, and Li+ could be stripped with the aqueous solution containing 0.2 mol L-1 HCl. In addition, the extraction efficiency of Li+ was almost not attenuated after 6 extraction cycles. This new extraction system shows a certain industrial application prospect for Li+ separation from the salt lake bine with high Mg/Li ratio.

Recovery of chromium (VI) from hazardous APV wastewater using a novel synergistic extraction system

As a well-known hazardous material, chromium (VI) in industrial wastewater has always attracted extensive attention. Many studies have focused on the recovery of Cr (VI) which is still challenging and received considerable interest. In this study, a novel synergistic extraction system using amide as extractant and Cyanex 272 as synergistic extractant was built to recover chromium (VI) from the APV wastewater. After optimizing the process parameters of extractant concentration, initial pH, extraction temperature, extraction time, extraction phase ratio, ammonia concentration and stripping phase ratio, the final extraction and stripping efficiency reached more than 99% and 98%, respectively. The Cr2O3 product with a purity of 99.52 was prepared and the organic phase could be effectively regenerated for recycling. The extraction mechanism of chromium (VI) in the synergistic extraction system was investigated in-depth with slope method, ESI-MS analysis and FT-IR analysis. In addition, molecular electrostatic potentials analysis was used to display visually the formation process of the extract complex. This paper offered a unique approach to guide sustainable chromium (VI) recovery from hazardous wastewater with great industrial and theoretical significance.

Mextral® 6103H/naphthenic acid/TOPO synergistic extraction system for recovery of nickel and cobalt from nickel laterite

Combination of the α-hydroxyoxime and the carboxylic acids results in synergistic extraction of nickel and cobalt and exhibits excellent performance of separating nickel and cobalt from manganese, magnesium and calcium, but they have the drawbacks of slow nickel stripping kinetics. In this study, trioctylphosphine oxide (TOPO), as an accelerator, was used to improve the nickel stripping kinetics of the Mextral 6103H/naphthenic acid system. The results showed that the addition of 0.35 M TOPO to 0.35 M Mextral 6103H/0.5 M naphthenic acid system significantly improved the nickel stripping kinetics. After mixing for 3 min, 96% stripping efficiency was obtained with 15 g/L H2SO4 at an O/A ratio of 1:1 and 25 ℃. The extraction pH isotherms revealed that more than 99.0% copper, 99% cobalt, 97% nickel and 86% zinc were extracted at pH 5.5, and only 6% manganese, 0.08% magnesium and 0.24% calcium were co-extracted. At pH 5.0, 87% calcium, 96% manganese and 97% magnesium can be scrubbed, resulting in 5.3 mg/L manganese and less than 0.5 mg/L magnesium and calcium remained in the scrubbed organic solution. Full stripping of nickel and cobalt could be achieved in two stages with 50 g/L nickel and 150 g/L H2SO4 at an O/A ratio of 10:1 and 25 ℃. Thus, compared with TBP, TOPO was more efficient for improving the nickel stripping kinetics at room temperature, which can reduce the power consumption and lead to clear production.

Modelling of lithium extraction with TBP/P507–FeCl3 system from salt-lake brine

• A thermodynamic model was developed for Li extraction by TBP/P507/FeCl 3 system. • The model parameters were optimized by fitting the calculated to experimental data. • Extraction mechanism was clarified by modelling species distribution in organic. Recovery of lithium from Mg-rich salt-lake brines by solvent extraction has been widely studied for high Li + /Mg 2+ selectivity and Li + extraction efficiency. In a previous study, a ternary synergistic solvent extraction system consisting of tributyl phosphate (TBP), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507, denoted as HL) and FeCl 3 was developed, in which high Li + selectivity and efficient Li + stripping simply with water were realized. In this study, to further elucidate the extraction mechanism of the TBP/P507/FeCl 3 system and minimize the efforts on the process optimization for Li extraction from Mg-rich salt-lake brines with different component concentrations from different sources, a thermodynamic empirical model based on mass balances and equilibrium equations has been developed. The model parameters were optimized by fitting the calculated data to experimental results. By calculating the distribution of species in the organic phase with the model, it was found that Li + primarily existed in the form of [Li(TBP) 2 ][FeCl 4 ], followed by [Li(TBP)][FeCl 4 ]. When Li + was stripped with water, Fe 3+ mainly existed in the form of FeCl 2 L·HL·2TBP in the organic phase at low O/A ratios but converted to [H(TBP) 2 ][FeCl 4 ] at high O/A ratios. This thermodynamic model provides a guide for the design of practical process flow.

Solvent extraction of Ni and Co from Ni-laterite leach solutions using a new synergistic system consisting of Versatic 10 acid, Mextral 6103H and Aliquat 336 with elemental mass balance for leaching, precipitation, solvent extraction, scrubbing and stripping

A new synergistic extraction system containing Versatic 10 acid, Mextral 6103H and Aliquat 336 was investigated for nickel and cobalt recovery from nickel laterite leach solutions. It was found that the addition of 0.3 M Aliquat 336 could significantly improve the nickel stripping kinetics of the Versatic 10 acid and Mextral 6103H mixed system, resulting in 98.9% stripping efficiency within 2 min. The effect of Aliquat 336 on the Versatic 10 acid (V10) and Mextral 6103H mixed system in terms of extraction and stripping performance was investigated. Based on the McCabe-Thiele plots for nickel/cobalt extraction and stripping, semi-continuous tests were conducted using the employed synergistic system. Over 99% nickel and 97% cobalt were extracted via a two-stage semi-continuous extraction with a pH profile of 4.5/5.0 for E1/E2 and an O/A ratio of 2.2, resulting in less than 2.0% manganese and negligible magnesium and calcium in the loaded organic solution. More than 95% co-extracted manganese was readily scrubbed via two stages of semi-continuous scrubbing, resulting in less than 1.0 mg/L Mn left in the scrubbed organic solution. Moreover, 98.8% nickel and 99.1% cobalt could be stripped using a two-stage semi-continuous stripping with 1.5 M H2SO4. Based on the test results, a proposed process flowsheet was developed for nickel and cobalt recovery and purification.

Synthesis of N-(2-ethylhexyl)-pyridine-4-carboxamide and its synergistic behaviors with dinonylnaphthalene sulfonic acid for the selective extraction of nickel and cobalt

The hydrometallurgical process for the recovery of nickel and cobalt requires a complex and expensive impurity removal process. Solvent extraction is widely used in industry for the separation, purification, and concentration of metals. However, current commercial extractants encounter some difficulties when cobalt and nickel are extracted from solutions containing a large amount of impurities such as manganese and calcium. There is an urgent need to develop new reagents for the selective extraction of Ni and Co. In this study, N-(2-ethylhexyl)-pyridine-4-carboxamide (NEHPCA) was synthesized, and the metal extraction capacity of its synergistic solvent extraction (SSX) system with dinonylnaphthalene sulfonic acid (DNNSA) and tributyl phosphate (TBP) modifier was examined. The experimental results show that the selectivity of the new SSX system has the order Cu > Ni > Co > Zn > Mn > Ca > Al ≈ Cr (III) ≈ Mg ≈ Fe (III), with excellent selectivity for nickel and cobalt. Using an organic phase composed of 0.7 M NEHPCA, 0.35 M DNNSA, and 0.2 M TBP under 1:1O/A operation, after three-stage theoretical extraction, more than 99% of nickel and cobalt can be recovered from a synthetic leaching solution of nickel laterite ore. Mechanistic studies showed that NEHPCA and water molecules participate in the internal coordination of metals, and DNNSA provided coordination anions to achieve charge balance, forming the Ni complex in this SSX system which existed most likely in the form of [Ni(NEHPCA)2(H2O)4](DNNS)2 in the organic phase.

Recovery of Chromium (Vi) From Hazardous Apv Wastewater Using a Novel Synergistic Extraction System

Recovery of Chromium (Vi) From Hazardous Apv Wastewater Using a Novel Synergistic Extraction System

A novel synergistic extraction system for the recovery of scandium (III) from sulfuric acid medium with mixed Cyanex923 and N1923

High extraction capability and outstanding selectivity are very attractive in the solvent extraction process. Scandium (Sc(III)), as a primary rare earth element (REE), generally lacks independent large-scale deposits and is mainly recovered as a by-product during the processing of mineral. However, the difficulty of stripping has been always a crucial problem to be solved in the scandium extraction system. This study aims to improve stripping performance while enhancing extraction efficiency for scandium. Herein, a novel synergistic extraction system for the recovery of scandium with a mixture of Cyanex923 (A, a mixture of four trialkylphosphine oxides) and N1923 (B, primary amine R1R2CHNH2) in sulfuric acid medium was put forward. The effect of the molar fraction (X) of Cyanex923 on the extraction of scandium was systematically investigated. The experimental results demonstrated that the coupled Cyanex923-N1923 exhibited an obvious synergistic effect on Sc(III). The maximum synergistic enhancement coefficient (Rmax) was calculated to be 2.20 when the molar fraction (X) of Cyanex923 was 0.4, and the H2SO4 concentration was 0.25 mol·L−1. Moreover, the synergistic extraction mechanism was discussed combined with multiple techniques including slope analysis method, FT-IR and NMR characterizations, to which the structure of extracted complexed was deduced to be Sc(SO4)1.5∙(A)0.5(B). Thermodynamic experiment was also explored in detail. More importantly, stripping with only 2 mol·L−1 HNO3 produced a relatively high stripping rate of 95%. The synergistic system still presented excellent reusability even after five treatment cycles. Finally, this study pointed out a potential industrial application value for the separation and recovery of Sc(III) from the sulfuric acid leaching liquor of nickel laterite ores.

Comprehensive recovery of metals in spent Ni–Mo/γ–Al2O3 hydrofining catalyst

This study proposes a technical route toward the comprehensive recovery of valuable metals from spent Ni–Mo/γ–Al2O3 hydrofining catalysts, which were employed to remove S, N, and O elements and metal–organic compounds from crude oil and petroleum products. Additionally, the process conditions are optimized, thereby providing good economic and environmental benefits. Sodium carbonate-assisted roasting of the spent catalyst effectively improves the secondary pollution and leaching effect. After Al, Mo, and Ni elements in the spent catalyst were converted into NaAlO2, Na2MoO4, and NiO, more than 99.8% of the metal ions entered the leaching solution, minimizing the loss. A synergistic extraction system using the di-(2-ethylhexyl)phosphoric acid (P204) and tri-n-octylamine (TOA) extractants were employed to extract molybdenum from the clarified acid leaching solution, and more than 97.5% of Mo was separated from Al and Ni. The MoO3 product was obtained by stripping with ammonia, followed by evaporating, and roasting. Furthermore, by adding ammonia to adjust the pH value of the molybdenum extraction solution to 4, 98.0% of the Al was extracted by P204. Subsequently, a Na2S precipitation agent was employed to convert Ni2+ into Ni(OH)S with a precipitation efficiency of 97.9%. Ultimately, the comprehensive recovery efficiencies of Al, Mo and Ni were 97.5%, 95.5%, and 90.9%, respectively, thereby realizing the comprehensive recovery of metals in the spent catalyst.