Solvent extraction of gold(I) from alkaline cyanide solutions by the cetylpyridinium bromide/tributylphosphate system

This paper explores the solvent extraction of KAu(CN)₂ from alkaline cyanide solutions using quaternary ammonium cetylpyridinium bromide (CPB) as an extractant with the addition of tributylphosphate (TBP) as a modifier. It also investigates the influence of several variables on gold extraction, including the molar ratio (β) of CPB to Au(I), the volume percentage of TBP (φ_TBP), NaCl concentration, phase ratio (AQ/ORG), and gold concentration in the aqueous phase. The results indicate that nearly all of the Au(I) (>98%) was transferred from the aqueous phase into the organic phase when β = 1 and φ_TBP = 30 vol%. We also carried out experiments for treating 20 L synthetic aurocyanide solution containing 10 mg/L Au(I) with column-shaped extraction equipment. The results demonstrated the recovery of more than 94.5% of Au(I) after two successive stages of extraction, and the Au(I) concentration in the raffinate was less than 0.5 mg/L. KSCN solution was used to strip the gold-loaded organic phase, and about 90% of Au(I) could be reverse extracted into the aqueous phase when the KSCN concentration reached 3.0 mol/L. The results obtained in this paper establish that the CPB/TBP extraction system has potential for practical application in the extraction and separation of gold from alkaline aurocyanide solutions.     

Solvent extraction and separation of palladium(II) and platinum(IV) from hydrochloric acid medium with dibutyl sulfoxide

The solvent extraction and separation performances of Pd(II) and Pt(IV) from hydrochloric acid solutions were investigated using dibutyl sulfoxide (DBSO) diluted in kerosene. Pd(II) was strongly extracted by a lower concentration DBSO in a lower concentration hydrochloric acid solution while the reverse was obtained for Pt(IV) extraction. Based on independent extraction and separation experiments of Pd(II) and Pt(IV), the separation parameters of Pd(II) and Pt(IV), including dibutyl sulfoxide concentration, contact time of aqueous and organic phases, organic/aqueous (O/A) phase ratio and H⁺ concentration of aqueous phase, were studied in detail, and the optimal separation parameters were obtained and summarized as the following: dibutyl sulfoxide concentration 0.6–1.2 mol dm^?3, organic/aqueous (O/A) phase ratio 0.6–1.0, H⁺ concentration of aqueous phase 1.0–1.5 mol dm^?3 and contact time of two phases 5 min. The as-prepared separation parameters were corroborated by the extraction and separation from a synthetic stock solution containing Pd(II), Pt(IV) as well as several common impurities like Fe(II), Cu(II) and Ni(II). The results revealed that Pd(II) could be separated efficiently from Pt(IV) with a high separation coefficient of Pd(II) an Pt(IV) (2.7 × 10⁴) by predominantly controlling dibutyl sulfoxide and hydrochloric acid concentrations. The extraction saturation capacity of Pd(II) was determined from 1.0 mol dm^?3 HCl solution with 3 mol dm^?3 dibutyl sulfoxide and its experimental value exceeded 14 g dm^?3 under the experimental conditions.Stripping of Pd(II) from loaded organic phase was performed using a mixed aqueous solution containing NH₄Cl and ammonia solutes. Pd(II) (99.2%) was stripped using the stripping solution containing 3% (m/v) NH₄Cl and 5 mol dm^?3 ammonia, respectively.     

Selective extraction of nickel from ammoniacal solutions containing nickel and cobalt by emulsion liquid membrane using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as extractant

The selective extraction and concentration of nickel from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membrane (ELM) technique using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as extractant has been presented. ELM consists of a diluent (kerosene), a surfactant (Span 80), an extractant (DBHQ), a modifier (tributyl phosphate), and a stripping solution (very dilute sulfuric acid solution containing EDTA as complexing agent, buffered at pH 4.25). Cobalt (II) in feed solution with 6 mol/L ammonia was oxidised to Cobalt (III) by H₂O₂ and pH of this ammoniacal solution was adjusted to 10.0 with the addition of hydrochloric acid (HCl). The important variables governing the permeation of nickel and their effect on the separation process have been studied. These variables were membrane composition, ammonia concentration in the feed solution, mixing speed, surfactant concentration, extractant concentration, pH of the feed and the stripping solutions, complexing agent concentration in the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99% of nickel from the ammoniacal solutions containing Ni and Co. The separation factors of nickel with respect to cobalt, based on initial feed concentration, have experimentally found to be of as high as 88.1 for about equimolar Co–Ni feed solutions.     

Leaching of atacamite (Cu2(OH)3Cl) using dilute sulphuric acid

The oxidised zone at the Mount Gunson, South Australia, copper mine contains copper in the form of atacamite. Copper at the Mount Gunson mine is currently being recovered by both heap and inplace leaching followed by cementation onto scrap iron. It was the purpose of this study to investigate the suitability of the ore to agitation leach processing. Agitation leaching was conducted at pH 2, and the results were subjected to kinetic analyses.     

Selective pressure leaching of Fe (II)-rich limonitic laterite ores from Indonesia using nitric acid

The selective extraction of nickel and cobalt over iron from an Indonesian limonitic laterite was investigated using nitric acid pressure leaching (NAPL). The mineralogical analysis showed that the major minerals were goethite and magnetite, and the content of the divalent iron was as high as 7.06%. Nickel and cobalt were mainly distributed in these two minerals; however, the distribution was non-uniform. A series experiments were conducted to examine the basic parameters and propose the optimal conditions for the extraction. When the ore was treated via HPAL under the optimal condition, the extracted nickel and cobalt were less than 75%, and the iron concentration in the leach liquor was over 12.5 g/L. By contrast, over 85% of nickel and cobalt were extracted and about 1.8 g/L iron was achieved using NAPL. The loss of nickel and cobalt can be mainly attributed to the undissolved magnetite and manganese minerals. The leaching process of NAPL is a dissolution–oxidation–precipitation mechanism, and in this process nitric acid acts as both a lixiviant and an oxidant. The formation of hematite results in a low iron concentration in the leach liquor without oxygen injected. Meanwhile, the oxidation and the precipitation of dissolved divalent iron results in a calculated savings in acid consumption of about 120 kg nitric acid per ton of ore can be obtained, which is equal to over 93 kg of sulfuric acid per ton of ore. Moreover, lower residual acid (20 g/L nitric acid) is a significant advantage of NAPL. The iron residues had a high iron content (>56 wt%) with no sulfur, making it suitable as raw materials for ironmaking.     

SO2-空气法从钴溶液中除铁、锰的试验研究

采用SO2-空气氧化沉淀法对刚果某铜钴矿浸出液中除铁、锰的工艺进行了试验研究,探讨了过程中各条件因素对氧化沉淀的影响规律。结果表明,在温度30℃,pH 3.5,混合气中SO2浓度2%的最佳工艺条件下,1 h内铁即氧化沉淀完全,而锰的氧化沉淀速率则相对较慢,6 h才达61.7%。除铁后液用碳酸钠沉淀可获得含Co>42%的粗制碳酸钴产品,可直接出售或进一步提纯钴。     

Combined extraction of metals and production of Mg(OH)2 for CO2 sequestration from nickel mine ore and overburden

Carbon storage by mineralisation (CSM) is an option for CO₂ emissions mitigation that has been under intensive study at Åbo Akademi (ÅA), Finland. Magnesium from silicate rocks is extracted with recoverable ammonium salts at 250–500 °C. The extracted elements are separated by selective precipitation and Mg is subsequently carbonated in a pressurised fluidised bed. This work studies the applicability of the process for co-extraction of Ni, Cu, Fe and Mg from nickel ore and nickel mine waste rock (overburden). The rock samples were collected from the Hitura Nickel mine, Finland. The results show that it is possible to co-extract the listed elements and integrate CSM (by the ÅA process) with steelmaking and Ni production industries.     

Extraction of cobalt(II) from an ammonium nitrate-containing leach liquor by an ammonium salt of di(2-ethylhexyl)phosphoric acid

A hydrometallurgical process that involves solvent extraction and selective precipitation has been used to selectively recover Co²⁺ from an aqueous filtrate containing mostly Co²⁺, NH₄⁺ and NO⁻₃ ions and trace amounts of Pt²⁺, Al³⁺ and Fe³⁺ ions. The effect of pH on the precipitation efficiencies of Al³⁺ and Fe³⁺ ions from the leach liquor was investigated. Solvent extraction exhibited good performance in terms of both Co²⁺ and Pt²⁺ ions extraction efficiency and phase separation when ammonium salt of di(2-ethylhexyl)phosphoric acid was used as an extractant in the presence of a tributylphosphate modifier. Cobalt was stripped from the organic phase with nitric acid to yield cobalt nitrate.     

The controlled oxidative precipitation of manganese oxides from Mn(II) leach liquors using SO2/air gas mixtures

In the future, an oxidation approach using SO₂/O₂ could be an important technique for extracting manganese from leach liquors. The aim of this work was to analyse the effect of temperature on the oxidative precipitation of Mn(II) in solutions derived from low-grade ore leaching using a SO₂/air gas mixture. This oxidation method is frequently used to eliminate Mn impurities from Ni and Co leach liquors. It was observed that controlling the temperature favoured the selective oxidation of Mn(II) to produce different oxidised species, such as MnO₂, α-MnOOH, γ-MnOOH and Mn₃O₄. The experimental results also showed that higher temperatures promoted the production of species with a lower manganese oxidation state. Moreover, in the range of studied operation variables, it was found that the best oxidation kinetics were obtained at pH = 6, 5% SO₂/95% O₂ and 75 °C. In addition, for efficiency reasons, a gas mixture flow rate of 200 mL/min is suggested.