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Review

Recent Hydrometallurgical Investigations to Recover Antimony from Wastes

by
Francisco Jose Alguacil
Centro Nacional de Investigaciones Metalurgicas (CSIC), Avda. Gregorio del Amo 8, 28040 Madrid, Spain
Metals 2025, 15(3), 276; https://doi.org/10.3390/met15030276
Submission received: 27 January 2025 / Revised: 19 February 2025 / Accepted: 24 February 2025 / Published: 3 March 2025
(This article belongs to the Special Issue Hydrometallurgical Processes for the Recovery of Critical Metals)
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Abstract

Antimony is a chemical element with diverse uses that falls into the range of a critical raw material. Although it appears in nature as stibnite, the mining of this mineralogical species is rare or uncommon, and it is the element that is basically recovered as a secondary material in the processing of various elements (such as gold and copper). Another source for the recovery of this element is the recycling of Sb-bearing wastes such as batteries and alloys. Once dissolved and in order to recover it from the different leachates, adsorption processes are the ones that seem to have, at least for the scientific community, the highest acceptance. This work reviews the most recent advances (in 2024) in the recovery of antimony from different sources using not only adsorption processes but also other technologies of practical interest.

1. Introduction

Without having the same level of popularity than other metals such as lithium, REEs, gold, niobium, tantalum, etc., but having the same label of a critical raw material [1], antimony is a key element in modern developments (including the military). Though nowadays this element (or its products) is basically used in lead alloys, lead–acid storage batteries and flame retardants, other potential uses are described in the literature [2].
Due to their properties (high theoretical capacity (660–1200 mA·h/g), stable working voltage and smooth charging/discharging platform), several Sb-based materials are ideally suited as anodes for Li/Na batteries [3,4,5]. Other uses of antimony include the development of Sb-based antiparasitic drugs (i.e., antileishmanial pentavalent antimonial drugs [6]) and the fabrication of advanced IR optics and magneto-optic devices [7].
The major mineral in which Sb occurs is stibnite, though this is not a common mineral and its mining tends to be rare. Another potential Sb supply wagon is the mining of precious metal (mainly gold) ores associated with, i.e., copper and other base metals. With an overall antimony mine production of about 83,000 tons in 2023 [8], China and Tajikistan are the main Sb producers from mining exploitations, with larger reserves located in China and Russia. Thus, the recycling of this element is of interest, and this recycling is mainly based on lead–acid batteries or lead alloys [9,10]. Antimony also is commonly found in anode slimes or in the electrolyte from copper electrorefining process [11].
With respect to Sb toxicity, it was demonstrated that occupational exposure to this element can cause lung toxicity, but it has no carcinogenic impact on humans [12].
The present work reviewed the most recent advances (in 2024) in the recovery-recycling of antimony (III) and (V) from different sources (such as raw materials and solid or liquid wastes). Though the work is focused on the application of hydrometallurgical methodologies (Figure 1), there is also space to comment on other methodologies (i.e., pyrometallurgy) of interest that have been applied in the recovery of this critical metal.
Generally, this hydrometallurgical process is carried out on oxidized species as a starting material; otherwise, using a previous thermal step is necessary to oxidize the raw or secondary material or using stronger oxidizing agents (i.e., ozone and concentrated acids). The leaching step uses different aqueous media, including acids and alkaline solutions. Once the element is dissolved, it often needs to be separates and/or concentrates from other undesirable elements present in the leachate. This separation or concentration is carried out by separation technologies, including adsorption (the most used in the present case), ion-exchange resins, liquid–liquid extraction, etc. Finally, antimony is recovered as any suitable product (oxide or metallic form).
The pyrometallurgical procedure involves the use of elevated temperatures and, in general, is expensive in terms of energy. Some drawbacks related to this methodology include the production of harmful gases and solid slags. Sometimes, as described below, a combination of pyro-hydrometallurgical procedures is used to recover antimony from a given starting raw or secondary material.

2. Leaching

In the mining industry, the management of the various tailings is a challenge with not always easy solutions. Thus, in order to provide a reliable procedure to treat Sb-bearing tailings (1.74% Sb) from the ETIBAKIR stibnite flotation plant of Haliköy (Turkey), a hydrometallurgical process for the recovery of antimony, arsenic, and iron and the removal of sulfide minerals from these tailings was developed [13]. The main mineral species were stibnite, pyrite, and a small amount of arsenopyrite, together with associated gangue minerals such as quartz and muscovite. Among the various experimental conditions used, best one was set as follows: 4.4 M HCl, 0.5 M NaNO3, 25% pulp density, 70 °C temperature, and 1 h reaction time. From the first laboratory scale tests to semi-pilot plant experiments, the leaching efficiencies were 99.9–98.3% Sb, 99.9–92.0% As, and 99.9–98% Fe. The final residue containing 91.4% SiO2 was sulfide mineral-free.
Based on the treatment of lead softening slag of Belgian origin (17.7% Sb), a pyro-hydrometallurgical process for selective arsenic removal and Pb and Sb recovery was developed [14]. The process consisted of an NaOH roasting (400 °C) step followed by water leaching, carbothermic reduction, and HNO3 leaching. This slag was first roasted with NaOH at 400 °C, followed by water leaching at room temperature; this operation solubilized arsenic as AsO43−. The arsenic-free slag was reduced with carbon (2.8% and 800 °C) for lead recovery as antimonial lead. Furthermore, the residual slag was leached with a 2.5 M HNO3 solution at 90 °C for two hours for the removal of residual lead and enrichment of antimony (64.7%), which was finally recovered as antimony trioxide after the thermal decomposition (200 °C) of the enriched leaching residue (Sb4O4(OH)2(NO3)2).
Using a chalcopyrite concentrate of Spanish origin (1.1% Sb) [15], microwave-assisted heating was used to resolve the problem of the poor solubilization of antimonial species when traditional heating processing was utilized. The optimal conditions to reach 95.7% antimony solubilizations were 250 g/L Na2S and 60 g/L NaOH as leaching agents, two hours and 140 °C, with microwave assistance. From the leachate (Sb2S42−), the recovery of antimony as metallic antimony by electrowinning or Sb2O3 via NaOH/H2O2 processing was considered.
Deep eutectic solvents (DESs) are types of chemicals with broad practical utility in different fields of interest, and this utility is based on their properties, such as low toxicity, cost-effectiveness, and environmental friendliness. Among these different utilities, these DESs are used as leaching reagents in a series of processes; thus, they are of potential interest for sustainable antimony recovery. In one investigation [16], a sample originally obtained from mining waste (6000 g Sb/ton) produced via the flotation of antimonite ore from the former Czechoslovakia was used to test various DESs (Table 1) as leachants for this element.
The best leaching efficiencies (100%) were obtained with the use of a ChCl:EG-based DES, four hours, 100 °C, and iodine as oxidizing agent. With respect to the amount of iodine used to reach this 100% effectiveness, there was an unexplainable mistake in this work. This mistake was due to that it was repeatedly mentioned in the text that 3 g of iodine is the correct amount to be used, and a close examination of Figure 6 in the published manuscript clearly indicated that this 100% effectiveness was reached with 4 g of iodine and not with 3 g (74.15% effectiveness).
The ore from the Iranian Sefid-Abe mine (Fe3Si2O5(OH)4·Sb3O6(OH)·Sb2O3) was used as source for the recovery of antimony [17]. The process utilized acidic or alkaline leaching followed by Sb-electrowinning. In the leaching step (8 h at 80–90 °C), antimony recovery efficiencies around 86% were derived from the use of 5 M NaOH or 5M HCl/5M H2SO4 media. Further, the electrowinning step using both acidic and alkaline leachates was investigated. In acidic medium, graphite and steel formed the anode and cathode, respectively. Other conditions were set up as a 2 V voltage, 0.1 A, and 30 °C, with severe corrosion of the steel cathode. Alkaline electrowinning also required 2 V at 0.5 A and 80 °C. In this case, the anode and cathode were of steel. After 6.5 h of run time, 97% or 89% of the antimony content of the respective alkaline or acidic solutions were deposited on the cathode.
Table 2 summarizes the main results obtained from this review of the leaching procedures carried out on various Sb materials.
As this review demonstrated and though not recently utilized, the leaching of some Sb-bearing raw materials (i.e., stibnite) needed the use of strongest and environmentally friendly oxidizing agents, and here ozone emerges as a candidate that fulfills both roles. However, there are still some drawbacks in its use to be solved, such as the somewhat low ozone production, the formation of by-products resulting from the use of ozone, etc. Other possibilities, though not recently described (in 2024) in the leaching of antimony-bearing materials, are bioleaching or the use of organic acids as leachants.

3. Adsorption

Anaerobic sludge obtained from a full-scale up-flow anaerobic sludge blanket (UASB) reactor treating brewery wastewater in Sonora (Mexico) was used to investigate the removal of Sb(III) and Sb(V) from synthetic solutions [18]. Moreover, biochar was added to the system in order to increase biological sulfate reduction to accommodate to the presence of high antimony concentrations in the solution. The experimental results indicated that higher metal concentrations (0.08–0.5 g/L Sb(III) and 0.2–1 g/L Sb(V)) presented better removal efficiencies than diluted antimony solutions (0.005–0.04 g/L Sb(III) and 0.005–0.1 g/L Sb(V)). Both biochemical and physicochemical reactions were responsible for the removal of at least 95% Sb(III) and 97% Sb(V) using biochar.
A Zr-based metal–organic frameworks (MIP-206) and its amine-modified material (MIP-206-NH2) for the recovery of antimony from both synthetic and actual mining wastewater (Nandan Tea Mountain mining area located in Hechi City, Huangxi Province of China) were developed [19]. The amine-modified material presented higher antimony uploads than the pristine MOF, 63.3 mg/g versus near 17.0 mg/g for Sb(III) and 102.2 mg/g versus 26.3 mg/g for Sb(V), despite the fact the amine-modified material presented a lower surface area than the pristine material: 1169.9 m2/g versus 1345.2 m2/g. Both MOFs presented a continuous loss of antimony (III) and (V) removal capacity with continuous use. In the work, it was not mentioned how antimony was recovered from metal-loaded MOFs. From the mining waste (pH 3.4) containing antimony, tin, lead, cadmium, and arsenic, treatment with an unidentified MOF resulted in a decrease in the antimony concentration from 2.48 mg/L to 0.08 mg/L.
Iron-coated cork granulates were used to evaluate their performance in antimony (III) and (V) recovery [20]. In continuous mode, the adsorption capacities were 13.0 mg/g and 10.0 mg/g for Sb(III) and Sb(V), respectively. However, an increase of the pH from 3 to 6 reduced the adsorption efficiency. Hydrochloric acid was effective for antimony desorption, but the iron that leached during desorption was a negative point in the usefulness of these adsorbents, since it poisoned the antimony desorption solution.
Although the desorption step must be considered as important as the adsorption one, by no means has it been as well researched as the latter. In the case of antimony (III) and (V) loaded onto very different materials, the most used desorbents are HCl (35%) and NaOH (34%), followed by NaCl and EDTA (9% each); citric (3%), ascorbic (2%), tartaric (2%), and nitric (2%) acids; and Na2HPO4 and MgSO4 (2% each) [21].
The treatment of acid mine drainage is an environmental necessity and a challenge since it can be used to form materials of potential environmental relevance. One of these materials is iron-based layered double hydroxides (LDHs) with sulfate intercalation, which are utilized to remove Sb(V) from solutions [22]. The experimental results indicated that using a dose of 1 g/L of the adsorbent, the antimony content (10.7 mg/L) of a solution at pH 3.7 decreased to 4.0 μg/L; however, the pH of the solution increased to a value of 8.1. Antimony was loaded onto the adsorbent via anion exchange between Sb(OH)6− species and the sulfate groups present in the adsorbent. Several desorbents were investigated, and among them 0.1 M NaOH or Na2CO3 solutions were the ones that presented the best efficiencies of 69% and 63%, respectively. Though the adsorbent performed well after four cycles of continuous use (more than 90% efficiency), there was a noticeable decrease in this efficiency in the 5th cycle (73%).
Activated carbon (Fe-Mn-SAC) prepared from Fe-Mn binary oxide-loaded sludge was utilized to remove Sb(V) from synthetic solutions [23]. The maximum adsorption efficiency was reached in the 3–5 pH value range with an increase in this efficiency as the temperature increased from 20 to 40 °C. Chemical adsorption was responsible for antimony loading onto the adsorbent. Using 2 M CaCl2 medium (2 h) and further washing with deionized water to desorb the metal, there was a continuous loss of adsorption efficiency with continuous use (six cycles).
An adsorbent for Sb(III) removal was obtained by cross-linking polyethyleneimine (PEI) onto phosphoric acid-modified lignin-based porous biochar (PPLB) [24]. The best adsorption capacity was obtained by the use of a 0.15 g/L adsorbent dosage and an aqueous pH value of 3. As an alternative to its continuous use to remove Sb(III) (with a slight decrease in the adsorption capacity up to three cycles), the Sb-loaded PPLB was recycled and valorized as a Sb/C composite of a sodium ion battery.
The widely utilized graphene oxide and chitosan as a GOCS matrix were modified with FeCl2 and four MnOx to form iron–manganese oxide (FM/GC) at a Fe/Mn molar ratio of 4:1 and were investigated to remove Sb(III) from aqueous medium [25]. The metal removal effectiveness followed the sequence MnSO4 > KMnO4 > MnCl2 > MnO2 (Table 3). With a maximum efficiency at pH 3, the increase in temperature in the 25–45 °C range favored antimony uptake onto the adsorbent (results based on the MnSO4-based composite). No data about the desorption step were available.
Also based on the Fe-Mn couple, a ferric–manganese oxide (FeMnOx) nanoparticle-embedded cellulose nanocrystal-based polymer hydrogel (FeMnOx@CNC-g-PAA/qP4VP or FMO@CPqP) was fabricated to remove both Sb(III) and Sb(V) from solutions [26]. In both cases, the adsorption efficiency was greatly pH-dependent, increasing from pH 2 to 6, and then decreasing from pH 7 to 12; thus, the maximum removal efficiencies were obtained at pH 6. The temperature (25–45 °C) influenced the adsorption efficiency in different ways: decreasing (Sb(III)) or increasing (Sb(V)) with the increase in this variable. Using a 0.1 M NaOH-NaClO solution to desorb any of the two Sb oxidation states, there was a continuous loss of efficiency with up to eight adsorption–desorption cycles. The adsorbent was used in the removal of antimony from wastewater from an electronic factory of Chinese origin. The FMO@CPqP hydrogel removed Sb with a 74.9% efficiency but also Cr (56.8%), Cu (43.3%), and Pb (50.9%).
Since there are some restrictions in the use of magnetite nanoparticles as an adsorbent mainly due to size issues, the addition of porous materials as mechanical supports can serve to improve the dispersibility of the nanoparticles. On this basis, acid-treated sepiolite was utilized as support material, and the acid–sepiolite-supported magnetite nanocomposite powder was fabricated to investigate its usefulness in the removal of Sb(V) from aqueous solutions [27]. Like in many systems, Sb(V) adsorption by the nanocomposite powder depended on the pH value, with the maximum adsorption reached at acidic conditions and decreasing with an increase in pH value. No data about the desorption step were available.
Starting from chitosan/iron sludge beads and using a pyrolytic procedure, magnetic chitosan carbon (MCC) was fabricated and used in the adsorption of Sb(III) from synthetic aqueous solutions [28]. Using this adsorbent, the variation of the pH from 3 to 10 had a negligible effect on the removal of this element. A 1 M NaOH solution could be used to desorb (50% efficiency) the adsorbed antimony.

4. Miscellaneous Operations

It was prospected the production of antimony as a by-product at the Olympias separation plant in Northern Greece. This plant works in skarn mineralization containing near 8% of boulangerite (Pb5Sb4S11) on the Pb concentrate [29]. The Sb-bearing mineralogical species can be separated from galena by froth flotation; furthermore, this concentrate can be hydrometallurgically treated for antimony recovery. It should be noted that no more explanations are given in the manuscript about the procedure used to recover this metal.
Difficulties in the separation of stibnite and arsenopyrite by flotation have led to the development of a Cu-KBX complex collector (based on the use of Cu2+ and potassium butyl xanthate (KBX)) to improve the separation of these two mineralogical species [30]. Micro-flotation experiments showed that by the use of this collector and at a pH of 5, the concentrate presented an antimony content of 61.08% in the presence of 4.65% of arsenic.
Based on a lead anode slime, a process for the preparation of antimony oxide was developed [31]. The process consisted of the oxidative transformation and vacuum separation of these slimes. In the oxidative step, both antimony and arsenic were converted to the As2O3 and Sb2O3 volatile compounds, where the arsenic species was separated in the vacuum step; in this step, the collected Sb2O3 (99.9% purity) contained valuable metals such as gold and silver.
In the copper electrorefining process, antimony and bismuth are concentrated in the solution and it is necessary to clean it from time to time. Cleaning is carried out by ion exchange resins, utilizing HCl to elute the metals loaded onto the resin. The recovery of these metals is of interest due to their value and for the reuse of the acidic solution. As an alternative to other procedures, the recovery and separation of antimony and bismuth from 6 M HCl acid solutions was investigated by the use of voltammetry and electrodeposition [32]. In potentiostatic mode, the preferential deposition of antimony takes place at −0.25 V Ag/AgCl, a value lying below the reduction potential of bismuth. Very high selectivity factors of antimony versus bismuth were reached by operating in galvanostatic mode at current densities of 1.5 mA/cm2 and a 4 molar Sb proportion in the solution composition, although it was found that this selectivity was Sb-concentration-dependent.
Similarly to the previous reference and based on the treatment of the eluate containing As, Sb, and Bi, a process aimed at the selective precipitation of antimony and bismuth was developed [33]. In this case, the eluate, provided by a Spanish company, consisted of 5 g/L Sb, 8 g/L Bi, 1 g/L As, 180 g/L HCl, and 17 g/L H2SO4. Prior to the As precipitation step, SO2 was bubbled onto the eluate in order to reduce all the arsenic and antimony present in the solution to their respective (III) oxidation state. In the precipitation step, antimony(III) was first precipitated at pH values around 1, and a further shifting of the pH to 2–2.5 produced the precipitation of bismuth. The precipitated species responded to the Sb4O5Cl2 and BiOCl stoichiometries. In a final step, Sb4O5Cl2 was precipitated as Sb2O3 (near 97% purity) by the use of NH3 or 5 g/L NaOH, whereas the precipitation of bismuth oxide (Bi2O3 98% purity) from the oxychloride salt only occurred using NaOH solutions in the 50–100 g/L concentration range.
As an extension of the previous reference, it was considered four scenarios to perform a techno-economic evaluation of antimony and bismuth recycling from the acidic eluates [34]. The four scenarios are the production of Sb4O5Cl2/BiOCl (scenario 1), Sb4O5Cl2/Bi2O3 (scenario 2), Sb2O3/BiOCl (scenario 3), and Sb2O3/Bi2O3 (scenario 4). Considering the evolution of the net present value (NPV) over the next 20 years, scenario 1 presented the best economic prospect with an NPV estimated as EUR 1,000,000, with a NPV over zero after nearly seven years. Scenario 3 also presented favorable estimations with an NPV around EUR 600,000 and NPV greater than zero after nine years. Both scenarios 2 and 4 did not reach an NPV over zero in the next 20 years.
Froth flotation was used to recover antimony from the Sefidabeh Sb deposit (Iran) [35]. In the process, stibnite was separated first, and the oxidized specimens were concentrated from the tailings of the first step by a second flotation unit.
A manganese cobalt MOF-based carbon nanofiber electrode (MnCo/CNF) was prepared and used as microbial fuel cell (MFC) anode, and pyrite was incorporated into the anode chamber (MnCoPy_MFC). Synergism between pyrite and MnCo/CNF facilitated total antimony (III) and (V) removal and energy generation in this latter composite [36].
The generation of arsenic antimony dust (HAAD) in lead smelters is an environmental threat that needs to be minimized. Since the dust is composed mainly of Sb2O3 and As2O3, a two-step vacuum volatilization–condensation procedure was developed to separate both oxides [37]. In the first step carried out at low temperature (420 °C), As2O3 was separated, and the dust that originated in the step was subjected to a second vacuum volatilization step, but in this case, using high temperatures (540 °C) to yield Sb2O3 and a lead–bismuth oxide as by-product.
Copper telluride slag produced in the copper smelting process was subjected to sulfurization and vacuum distillation to recover the metals (antimony among them) contained in it [38]. In the sulfurization step, the oxygen associated with antimony (also copper and arsenic) was removed and Sb2S3 was formed. Under vacuum, 68.77% of antimony in the volatiles was found.
The so-called noble antimony contains precious metals in the antimony smelting system, and this is why it has a high added value. This noble antimony can be purified, and at the same time recover the precious metals, by a vacuum gasification process [39]. An increase in the temperature produced a remarkable recovery of the three elements in the volatile or residue fractions (Table 4).
Crude antimony (99.865% purity) of Chinese origin was used to produce a high-purity metal via two processes: low temperature–high temperature vacuum distillation (LHVD) or high temperature–low temperature vacuum distillation (HLVD) [40]. Under the LHVD conditions of 1–10 Pa, time of 90 min, and a low-temperature stage in the 500–600 °C range, Mg, Bi, Zn, and Cd volatilized, whereas Sb, Ag, Au, and Cu remained in the residue. This residue was subjected to a second high-temperature stage in the 650–900 °C range at 1–10 MPa, yielding 4 N antimony as volatile fraction and a residue containing high-boiling-point impurities. The HLVD process consisted of a first step at 1–10 MPa and 650–900 °C to yield volatiles (antimony and low-boiling-point impurities) and residue (high-boiling-point impurities) fractions, and the processing of the volatile fraction in a second step at 1–10 MPa and 500–600 °C produced a volatile fraction containing low-boiling-point impurities and a residue consisting of a 4 N antimony product.
Among the myriad of species with a potential usefulness to remove contaminants from liquid effluents, electro-generated atomic hydrogen (H*) is gaining importance. However, certain shortcomings in its utilization, i.e., a short life span and confinement to the electrode–solution interface, has restricted its applications. To overcome these shortcomings, palladium nanoparticles loaded onto a carbon cloth (Pd/CC) electrode are being developed both to stabilize surface atomic H* and improve its electroreduction performance against, i.e., antimony(III) [41]. With respect to the pristine carbon cloth electrode, the Pd/CC electrode showed a 0.4 V increase in the onset potential of H* electroreduction together with a 5.5-fold improvement in the electrochemically active surface area. In the case of antimony(III) removal, in the reduction of this oxidation state to the zero valent state, the removal rate constant was increased by 2.2-fold, whereas the formation of metallic antimony on the electrode surface was increased by 5.1-fold. The pH of the solution influenced the removal efficiency in the order of 1 = 3 > 5 > 7 > 9.
A slag containing B2O3-Al2O3-CaO-SiO2, characterized by a low melting point, was used to carry out matte smelting for concentrating antimony in a low-grade antimony concentrate (simulated) [42]. The process eliminated major impurities, particularly quartz. The optimal conditions for the metal recovery rate were set as a temperature of 1050 °C, a WSiO2/W slag ratio of 40/100, and a basicity of 0.5. Under these conditions, the direct removal rate of antimony reached 91.16%, being 2.34% the value of the concentration of antimony in the slag. The end-matte containing about 53.3% antimony can be oxidized to Sb2O3 following a conventional oxidative volatilization procedure; furthermore, this product can be reduced to yield crude antimony (98.01% purity).
Using a fluidized-bed reactor, the removal of antimony(III) from a synthetic solution was investigated [43]. The system was feed from the reactor bottom with antimony and tartaric acid solutions together with Sb2O3 seed crystals. The presence of tartrate ions competing with OH− to complex with antimony(III) mediated the formation of a crystal structure. The granulation and antimony removal efficiencies were pH-dependent (Table 5).
Granulation increased from pH 7 to 9 and then decrease at higher pH values, whereas the removal of antimony(III) followed the same sequence. The highest granulation (91%) and removal (94%) efficiencies were reached at pH 9. The TA/Sb(III) molar ratio also affected these two parameters; at a TA/Sb(III) molar ratio of 2–2.5, both granulation and metal removal reached the maximum effectiveness. With respect to the seed characteristics, both granulation and recovery reached the maximum values at a seed concentration of 6 g/L and seed size in the 13–38 µm range. An up-flow velocity of 42 m/h and a hydraulic retention time of 40 min were also responsible for the highest granulation and antimony removal efficiencies.
An antimony sulfide concentrate was used as starting material to recover both sulfur and the metal itself [44]. The concentrate was subjected to a series of steps consisting of (i) desulfurization at 900 °C and (ii) molten salt (NaCl-KCl) electrolysis (900 °C, 20 A, six hours) of the product obtained in the previous step, where the products of this second step are fumes, crude antimony C, and a rich Sb2S3 molten salt that was subjected to a further (iii) step. This third step was a constant-voltage electrolysis step (900 °C, 3 V, and three hours), yielding fumes, crude antimony V, and a poor Sb2S3 molten salt. This last residue was treated to regenerate the molten salt, whereas the fumes from steps (ii) and (iii) were collected to yield sulfur. Also, crude antimony from steps (ii) and (iii) was collected to produce high-purity antimony after oxidation-based refining of the crude antimony fraction.

5. Conclusions

This review showed that once antimony is dissolved (from the respective raw material or solid waste and preferably in acidic medium), adsorption processing is considered the most attractive and practical approach for the recovery of this element (both in its (III) or (V) oxidation states) from the various aqueous media. This attractiveness is attributable to its operational simplicity, cost-effectiveness, high efficiency, and less sludge production. Making a comparison between the different adsorbents is not as simple as it appears since the experimental conditions (temperature, adsorbent dosage, pH of the solution, and initial metal concentrations) are not the same. However, from a qualitative point of view, Table 6 summarizes the maximum loadings using the various reviewed adsorbents.
These results showed the wide range of Sb loadings on the different adsorbents, and Sb(V) presented higher loadings than Sb(III) [17,24].
Most of these adsorbent are investigated at the laboratory scale; thus, data to know its real performance are still absent. These data must be derived from pilot tests in a continuous scale (column) and using real solutions from the leaching of Sb-bearing raw or secondary sources. Also, this adsorption step must be matched with resulting solutions from the leaching step, feeding the adsorption step, and solutions exiting this adsorptive step feeding a final step to yield the ending antimony product.
At this point, it should be mentioned that a number of the reviewed manuscripts did not include data on the desorption step. Thus, the real performance of these adsorbents are unknown, even at the laboratory scale.
The development of new adsorbents must be a key point in future investigations; however, these adsorbents, especially those incorporating metals to increase the uptake capacity, need to be stable in the desorption conditions. This review realized that in many cases, there is a continuous loss of the metal-adsorption capacity under continuous (cycles) use.
Due to their environmental friendliness, the use of DESs as alternatives to conventional leaching reagents must be another point for future investigations.
Also, the coupling of pyrometallurgical–hydrometallurgical processes must be another hot point for future investigations. This can be of importance when refractory ores needed to be processed.
The development of other hydrometallurgical operations, i.e., liquid–liquid extraction and ion exchange resins, are of interest due to their versatility to treat complex metal solutions or higher-concentration metal solutions in the case of liquid–liquid extraction.
Finally, life cycle control analyzing the environmental impacts of these processes to avoid future environmental crises is another point to consider in order to find the best antimony (and, in general, other metal) recovery process.

Funding

This research received no external funding.

Acknowledgments

To the CSIC (Spain) for support.

Conflicts of Interest

The author declared no conflicts of interest.

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Metals 15 00276 g001
Figure 1. Main hydrometallurgical operational units.
Figure 1. Main hydrometallurgical operational units.
Metals 15 00276 g001
Table 1. The various DESs used in the leaching experiments.
Table 1. The various DESs used in the leaching experiments.
HBAHBDHBA:HBD Molar Ratio
Choline chloride (ChCl)Ethylene glycol (EG)1:2
Choline chloride (ChCl)Malonic acid (MA)1:1
Choline chloride (CHCl)Thiourea (U)1:1
HBA: hydrogen bond acceptor. HBD: hydrogen bond donor. Adapted from [16].
Table 2. Summary of the leaching procedures used for Sb materials.
Table 2. Summary of the leaching procedures used for Sb materials.
Sb SourceLeaching Conditions% Sb Leaching RateFinal ProductRef.
Sb tailings4.4 M HCl + 0.5 M NaNO3, 70 °C, 1 h99Not described[13]
Chalcopyrite concentrate250 g/L Na2S + 60 g/L NaOH, 140 °C, 2 h, microwave assisted96Sb2O3[15]
Mining wasteChCl-EG-based DES, 100 °C, 4 h, iodine assisted100Not described[16]
Sb oreAlkaline or acidic leaching, 80–90 °C, 4 h86Metallic Sb[17]
Table 3. Adsorption efficiencies of the Fe-Mn composites.
Table 3. Adsorption efficiencies of the Fe-Mn composites.
Mn Compound% Sb Adsorption Removal
MnSO463.96
KMnO460.2
MnO238.98
MnCl247.74
pH: 3. Temperature: 25 °C. Time: two days. Adapted from [25].
Table 4. Sb, Au, and Ag recoveries in the vacuum gasification process.
Table 4. Sb, Au, and Ag recoveries in the vacuum gasification process.
Temperaturea Sbb Aub Ag
600 °C1000 °C95.7%98.5%1300 g/t10100 g/t190 g/t1900 g/t
a In the volatiles. b In the residue. Adapted from [39].
Table 5. Influence of the pH on the granulation and Sb removal efficiencies.
Table 5. Influence of the pH on the granulation and Sb removal efficiencies.
pHGranulationSb Removal
765%66%
991%94%
1079%90%
Adapted from [43].
Table 6. Maximum Sb loadings using different adsorbents.
Table 6. Maximum Sb loadings using different adsorbents.
ElementAdsorbenta Maximum Loading, mg/gRef.
Sb(III)Pristine MIP-20618.8[17]
MIP-206-NH268.9[17]
Iron-coated cork8.2[18]
PPLB371.6[22]
FM/GC-SO4Mn178.8[23]
FMO@CPqP276.1[24]
Sb(V)Pristine MIP-20628.9[17]
MIP-206-NH2111.1[17]
LDHS7.2[20]
FMO@CPqP286.8[24]
a Based on the Langmuir model.
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Alguacil, F.J. Recent Hydrometallurgical Investigations to Recover Antimony from Wastes. Metals 2025, 15, 276. https://doi.org/10.3390/met15030276

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Alguacil FJ. Recent Hydrometallurgical Investigations to Recover Antimony from Wastes. Metals. 2025; 15(3):276. https://doi.org/10.3390/met15030276

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Alguacil, Francisco Jose. 2025. "Recent Hydrometallurgical Investigations to Recover Antimony from Wastes" Metals 15, no. 3: 276. https://doi.org/10.3390/met15030276

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Alguacil, F. J. (2025). Recent Hydrometallurgical Investigations to Recover Antimony from Wastes. Metals, 15(3), 276. https://doi.org/10.3390/met15030276

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