Beneficiation of a Nigerian sphalerite mineral: Solvent extraction of zinc by Cyanex®272 in hydrochloric acid
Research highlights
► Extraction of Zn(II) from sphalerite leach liquor in HCl by Cyanex 272. ► Fundamental studies adopted to Zn(II) recovery from sphalerite leachate. ► Combination of precipitation, cementation, roasting, calcination adopted for Zn(II) and ZnO recoveries. ► A practicable hydrometallurgical flow diagram proposed.
Introduction
Zinc is mostly extracted from sphalerite (ZnS) ore. Deposits of zinc and lead ores including sphalerite which are usually found as mixture have long been known in Nigeria, but they have only been mined in the past on a very small scale. An estimated 10 million tonnes of zinc/lead veins are spread over eight states of Nigeria. Proven reserves in three prospects in the East-central areas are 5 million tonnes. (Min. and Ind., Nigeria, 2010). In the commercial flow sheet for the production of zinc metal, the sphalerite concentrate is roasted, leached in sulphuric acid and electrolyzed (Alguacil and Martinez, 2001). Zinc is used in metallic coating to improve corrosion resistance of various types of steel. The pickling of steel goods is usually carried out using 10–20% HCl (Regel et al., 2001).
Zinc is primarily produced from sulphidic ores including sphalerite, ZnS. Other sources of zinc include oxide-carbonate ores and different secondary sources such as zinc ash, zinc dross, flue dusts of electric arc furnace, leach residues, etc. Pyrometallurgical and hydrometallurgical routes or combination of the two can be employed for treating secondary materials (Turan et al., 2004). The hydrometallurgical process has been established to be more eco-friendly for treating such materials having low zinc content (Leclerc et al., 2003).
In recent years, the recovery of metals from aqueous chloride solutions has attracted much attention. This is due to the high efficiency of the chloride leaching processes, which are now recognised as a logical choice for treating complex sulphide ore concentrates which cannot be easily or economically treated by other means. Another important aspect of such leaching process is that sulphur is liberated in the elemental form rather than as sulphur dioxide (Cote and Jakubiak, 1996).
In hydrometallurgical processes, valuable metals are generally recovered by a combination of two or more of leaching, precipitation, solvent extraction and electrowinning techniques. During leaching, dissolution of metals with a suitable acid or mixture of acids is possible. The processing of leach liquor solutions containing different concentrations of acid/acids is very complex and separation of the metal ions using various techniques such as precipitation, adsorption, solvent extraction, ion-exchange, etc. can be cumbersome (Sarangi et al., 2007). Of these purification technologies, solvent extraction shows a prominent role as a separation (and concentration) operation within these processes (Alguacil and Martinez, 2001) .
In this regard, the use of organophosphorus extractants in solvent extraction of metals has been steadily increasing because of their excellent selective nature in forming complexes under specific conditions. In particular, the introduction of diakyl phosphoric and phosphoric acids including Cyanex 272 has brought about a vast change in the separation technology (Daoud et al., 2006, Kunungo and Mohapatra, 1995). Thus, Cyanex 272 has been regarded as better reagent for the zinc extraction and very selective for the removal of other metal ions including cobalt to avoid possibility of cross contamination of reagents and has been adopted at the Murrin Murrin plant in Western Australia (Flett, 2005).
In the particular case of chloride-based zinc hydrometallurgy, a number of investigations using different extractants have been reported (Alguacil et al., 1992, Benito et al., 1996, Jia et al., 2002, Li et al., 2003, Mellah and Benachour, 2007). In most of these studies, synthetic solution containing Zn(II) was used and possible efforts in separating Zn(II) from other metal ions have been undertaken with respect to the extraction mechanism and the extracted complexes being formed. The results of some of these investigations are summarised in Table 1.
As evident from Table 1, there is a very limited work on the extraction of Zn from an aqueous leach liquor emanating from sphalerite mineral, (Baba et al., 2004).
The first part of the studies on the beneficiation of the sphalerite mineral had earlier been published (Baba and Adekola, 2010). The present investigation constitutes the second part and it is focused on the extraction and separation of zinc(II) from associated impurities such as lead, iron, Cu, Ag etc., contained in Nigerian sphalerite mineral. This is a first in-depth study on the hydrometallurgical recovery of zinc and lead from a Nigerian sphalerite origin using Cyanex 272.
Section snippets
Experimental
The experimental approach adopted for this study comprises a preliminary work aimed at establishing conditions for the optimal extraction of Zn from synthetic Zn(II) solutions by Cyanex 272 with subsequent application to the recovery of zinc from sphalerite leachate. The leachate obtained from the leaching of 10 g/L sphalerite per litre of 4 mol/L HCl solution at 80 °C for 120 min (Baba and Adekola, 2010) was used for the systematic study of the extraction of Zn(II) and Pb(II). The leachate has the
Influence of initial metal ion concentration
Solutions containing different concentrations of Zn(II) within the range of 0–300 mg/L dissolved in HCl solution whose pH was 3 were prepared (Baba, 2008, Baba et al., 2009). The extraction was studied by 4.17 × 10− 2 mol/L Cyanex 272 in kerosene at 25 °C ± 2 °C for 25 min (Daoud et al., 2006). The results obtained are represented in Fig. 1.
It is clear from Fig. 1 that the increase in the initial concentration of Zn(II) is accompanied by an increase in the extraction process before tending to a constant
Conclusions
The results on fundamental studies on solvent extraction of synthetic solutions of Zn(II) showed that extraction of metal ions increased with increasing pH, extractant concentration, and temperature. The stoichiometry of the extracted metal species by Cyanex 272 with Zn(II) was found to be ZnA2. The apparent standard molar enthalpy (∆H°), molar entropy(∆S°) and Gibb's free energy(∆G°) of 26.81 kJ/mol, 107.63 J mol–1 K–1 and − 5.48 kJ/mol were calculated for the process, respectively. These values
Acknowledgements
The authors wish to thank Dr. Oliver Rouher and Mrs Christine Salomon of Cytec Industries, Rungis Cedex, France, for their benevolence by supplying Cyanex 272. A. A. Baba also thanks the University of Ilorin, Ilorin-Nigeria, for the 2005/2006 Staff Development Award for Ph.D research in Chemistry; and the Academy of Sciences for the Developing World (TWAS), Trieste, Italy for the 2010 CSIR-TWAS Fellowship for Postdoctoral Research at Institute of Minerals and Materials Technology,
References (36)
- et al.
Study of the extraction of Zinc(II) in aqueous chloride media by Cyanex 302
Hydrometallurgy
(1992) - et al.
Hydrometallurgical processing of a Nigerian Sphalerite in hydrochloric acid: characterization and dissolution kinetics
Hydrometallurgy
(2010) - et al.
Development of a combined pyro-and hydro-metallurgical route to treat spent zinc-carbon batteries
J. Hazard. Mater.
(2009) - et al.
Extraction equilibria of Zn(II) in aqueous chloride media by Cyanex 302 in Toluene
Hydrometallurgy
(1996) - et al.
Cementation of metal removal in zinc electrowinning circuits
Min. Eng.
(2005) - et al.
Modelling of extraction equilibrium for zinc (II) extraction by a bibenzimidazole type reagent (ACORGA ZNX 50) from chloride solutions
Hydrometallurgy
(1996) - et al.
Solvent extraction separation of Zn(II), Fe(II), and Cd(II) using tributylphosphate and CYANEX 921 in kerosene from chloride medium
Chem. Eng. Process.
(2008) - et al.
Stripping of copper from Cyanex®301 extract with thiourea hydrazine sodium hydroxide solution
Hydrometallurgy
(2007) Solvent extraction in hydrometallurgy: the role of organophosphorus extractants
J. Organomet. Chem.
(2005)- et al.
Solvent extraction of zinc from ammoniacal/ammonium chloride solutions by a sterically hindered ß-ketone and its mixture with tri-n-ctylphophine oxide
Hydrometallurgy
(2010)
Coupled transport of Zn(II) through a supported liquid membrane containing bis (2,4,4-trimethylpentyl)phosphonic acid in kerosene II. Experimental evaluation of model equations for rate process under different limiting conditions
J. Membr. Sci.
Hydrometallurgical extraction of zinc ferrites
Hydrometallurgy
Defining the paragoethite process for iron removal in zinc hydrometallurgy
Hydrometallurgy
Selective extraction of zinc(II) over iron(II) from spent hydrochloric acid pickling effluent by liquid–liquid extraction
J. Hazard. Mater.
The solvent extraction of zinc, cadmium and chromium from phosphonic acid solutions by tri-n-butyl phosphate in kerosene diluent
Sep. Purif. Tech.
Seperation of iron(III), copper(II) and zinc(II) by TBP, LIX 841 and Cyanex 923
Sep. Purif. Technol.
Extraction of Zn(II) from aqueous hydrochloric acid solutions into alamine 336-m-xylene systems modeling considerations to predict optimum operational conditions
Hydrometallurgy
Recovery of zinc and lead from zinc plant residue
Hydrometallurgy
Cited by (32)
Performance evaluation during extraction technique in modified rotating disc column: Experimental and mathematical modeling
2022, Chemical Engineering and Processing - Process IntensificationCitation Excerpt :The several benefits especially less expensive setup, more product purity, and wide selectivity are the features of the solvent extraction method [7]. In recent decades, different acidic extractants such as D2EHPA [8], PC-88A [9], Cyanex272 [10], Cyanex302 [11], and Cyanex921 [12] have been commonly suggested for Zn (II) extraction from sulfate medium. Jafari and co-workers investigated the selective extraction of zinc from manganese and cadmium in the hydrochloric acid media using D2EHPA [13].
Pb-Zn recovery from a malic leach solution of a carbonate type ore flotation tailing by precipitation and solvent extraction
2021, Separation and Purification TechnologyIntensified extraction and separation of zinc from cadmium and manganese by a slug flow capillary microreactor
2021, Separation and Purification TechnologyOrganophosphorous extractants for metals
2021, HydrometallurgySolvent extraction of zinc from synthetic Zn-Cd-Mn chloride solution using D2EHPA: Optimization and thermodynamic studies
2018, Separation and Purification TechnologyCitation Excerpt :Hence, the recovery of zinc from tailings and secondary resources has recently been developed. The efficient purification of these zinc solutions has been considered by the solvent extraction process [7–11]. Also, in industrial cases such as Zincex, modified Zincex, Zincolar and CENIM-LNETI processes, this method is used to purify and concentration of the zinc solutions which are obtained from leaching process [10,12–14].