Atmospheric leaching characteristics of nickel and iron in limonitic laterite with sulfuric acid in the presence of sodium sulfite

Atmospheric leaching of nickel from limonitic laterite ores is regarded as a promising approach for nickel production, despite its low nickel recovery and slower leaching rate than high pressure acid leaching. Sulfur dioxide can enhance the sulfuric acid leaching of laterite, but its behavior for enhancing atmospheric sulfuric acid leaching was uncertain due to SO₂ losses and emission. In this study, sodium sulfite was used as a substitute for SO₂ gas in the leaching and the sulfuric acid leaching characteristics of Ni and Fe from a limonitic laterite in the presence of sodium sulfite were investigated. A linear correlation exists between the extraction of Ni and Fe, indicating the difficulty in selective leaching of Ni over Fe. Most nickel is isomorphically substituted within the goethite and it is difficult to dissolve in a high oxidation–reduction potential solution environment, resulting in a low nickel recovery. SO₂(aq) generated from the reaction of sodium sulfite in sulfuric acid solution, lowers the potential for the reducing reaction of FeOOH to give Fe²⁺, accelerating the iron extraction and nickel liberation from goethite.     

Agglomeration and column leaching behaviour of goethitic and saprolitic nickel laterite ores

Processability of complex, low-grade nickel (Ni) laterite ores via heap leaching is very limited due to some intractable geotechnical and hydrological challenges such as poor heap porosity/permeability and structural stability. This work presents some investigations on laboratory batch drum agglomeration and continuous column leaching behaviour of saprolitic (SAP) and goethitic (G) Ni laterite ores as part of the quest for an effective ore pre-treatment process for enhanced heap leaching. As a focus, the effect of ore mineralogy/chemistry on the agglomeration and column leaching behaviour of −2 mm (crushed from −15 mm run-of-mine) G and SAP Ni laterite ores was examined. To produce ∼5–40 mm agglomerates in <15 min, the SAP ore required a higher H₂SO₄ (30 wt.%) binder dosage compared with the G ore, although both ores displayed substantially similar, coalescence-controlled agglomeration mechanism. The resulting G agglomerates were more robust than the SAP ones based upon their compressive strength and acidic solution soak test measurements. However, over 100 days of continuous column leaching, the structural stability of the SAP agglomerate bed was slightly greater than that of G agglomerates, reflecting a lesser slump of the former. The pregnant leach solution analysis revealed greater Ni/Co extraction rates from the SAP than the G agglomerates. Whilst the total mass of acid consumed per ton dry ore processed was greater for the SAP ore, the total kg acid per kg Ni extracted was markedly lower. Incongruent leaching of gangue minerals’ constituent elements (e.g., Fe, Mn, Mg, Al and Si) occurred and contributed significantly to the overall acid consumption. The findings show the relevance of agglomeration and column leaching tests for providing useful information for plant designing and optimization of Ni laterite heap leaching operations.     

Leaching of limonitic laterite ore by acidic thiosulfate solution

Cobalt is usually recovered as a by-product of copper and nickel processing, and only a small amount of cobalt is derived from laterites although a vast majority of cobalt resources in them. The exploitation of limonitic laterite containing high content of cobalt is becoming increasingly important. The mineralogy of a limonitic laterite ore was characterized by environmental scanning electron microscope (ESEM) and X-ray diffraction (XRD) in this paper. The results show that nickel occurs in goethite mainly, while cobalt is predominantly associated with manganiferous minerals. Thiosulfate is found to be able to selectively leach cobalt from limonitic laterite in the presence of sulfuric acid, and 91% Co, 22% Ni, 10% Fe are leached from an ore containing 0.13% Co, 1.03% Ni within the first 5 min at 90 °C under the conditions of 10 g/L sodium thiosulfate, 8% (w/w) sulfuric acid and 10:1 L/S ratio. The leaching kinetics of Mn and Co by acidic sodium thiosulfate solution can be characterized by the Avrami equation. In acidic solution, thiosulfate readily decomposes into sulfur and sulfur dioxide as intermediary reagents to reduce pyrolusite (MnO₂) and goethite (FeOOH); therefore, nickel and cobalt associated with goethite and pyrolusite respectively are extracted due to reduction dissolution. Furthermore, cobalt is selectively leached over iron and nickel because pyrolusite is preferentially reduced by acidic thiosulfate rather than goethite. The novel process may give an alternative method to selectively recover cobalt as the primary product from limonitic laterites at atmospheric pressure.     

褐铁矿型红土镍矿硫酸高压浸出的研究

研究了褐铁矿型红土镍矿硫酸高压浸出过程中浸出温度和时间、硫酸用量对镍、钴、锰、铁、铝、镁、硅、铬浸出的影响。在浸出温度为250℃,浸出压力3.9 MPa,浸出时间为40 min,硫酸用量240kg/t干矿的优化条件下,镍,钴,锰的浸出率分别为96.8%,96.6%,98.7%,铁、铝、镁、硅的浸出率分别降低到2.6%,16.9%,61.8%,1.9%,铬的浸出率降低到0.7%,浸出液中的铬以Cr~(3+)的形式存在,浸出液中没有Cr~(6+)。静置分离试验表明,在此浸出条件下的浸出矿浆固液分离效率较高。扫描电镜分别对30、40、60 min浸出渣相微观形貌的分析表明,浸出30 min时针铁矿中Fe~(3+)绝大部分溶出并经过水解重新沉淀,延长浸出时间只是使铁相的等粒-圆粒状颗粒分布趋于均化。浸出渣相的主要成分为Fe_2O_3,(H_3O)Al_3(OH)_6(SO_4)_2,KAl_3(SO_4)_2(OH)_6及Si O_2。     

Innovative technology for processing saprolitic laterite ores by hydrochloric acid atmospheric pressure leaching

An innovative technology for processing saprolitic laterite ores from the Philippines by hydrochloric acid atmospheric leaching and spray hydrolysis is proposed. The factors that affect the hydrochloric acid atmospheric leaching of the laterite ores and spray hydrolysis of the atmospheric acid leach solution are investigated. Experimental results show that the leaching of Ni, Fe, and Mg is 98.9 wt%, 97.8 wt%, and 80.9 wt%, respectively, under optimal acid leaching conditions. The hydrolysis of Ni and Fe by the atmospheric acid leach solution approaches 100 wt% at the temperature range of 450–500 °C. Characterization results show that a serpentine mineral, nominally Mg₃Si₂O₅(OH)₄, is the major component and goethite, FeO(OH), is the minor one in the laterite ores. Treatment by hydrochloric acid atmospheric leaching breaks the mineral lattices of the laterite ores and makes amorphous silica the primary product in the atmospheric acid leach residue. The grade of Ni in the hydrolyzate increases to 4.55%. The hydrolyzate with high Ni content can be utilized for ferro-nickel production.     

The effect of sodium sulphate on the hydrogen reduction process of nickel laterite ore

A series of nickel laterite ores with different calculated amounts of anhydrous sodium sulphate were prepared by physical blending or sodium sulphate solution impregnation. The reduction of the prepared nickel laterite ore by H₂ was carried out in a fluidised-bed reactor with provisions for temperature and agitation control, and the magnetic separation of the reduced ore was performed using a Davis tube magnetic separator. The mineralogical properties of the raw laterite ore, reduced ore and magnetic concentrate were characterised using ICP, TG–DSC, N₂ adsorption, X-ray diffraction and optical microscopy. The catalytic activity of sodium sulphate was also studied by using Hydrogen temperature-programed reduction. The experimental results indicate that Na₂SO₄ could overcome the kinetic problems faced by the laterite ore and that it exhibited noticeable catalytic activity only if the temperature reached at least 750 °C. This high temperature accelerated the crystal phase transition of the silicate minerals and increased the utilisation of H₂. In comparing the results from the two different methods for adding Na₂SO₄, the nickel content and recovery of the magnetic concentrate were increased by using the impregnation method rather than the physical blending method and the increasing amount of sodium sulphate assisted in the further beneficiation of nickel. The partial pressure of H₂ and the reducing time also affected the reduction process of the iron oxides. The results of the microscopic study indicated that the formation of a Fe–S solid solution, which was derived from the SO₂ sulphide reduction of FeO, was conducive to mass transfer and accelerated the coalescence of metallic ferronickel particles. For the nickel laterite ore, under the synergistic effect of sodium sulphate and hydrogen, a nickel content and nickel recovery of 6.38% and 91.07% were obtained, respectively, with high product selectivity.     

Effects of sodium tripolyphosphate and sodium carbonate on the selective flocculation of diasporic-bauxite in the presence of calcium and magnesium ions

In this study, sedimentation tests for individual minerals and artificially mixed minerals and bauxite ores were carried out to understand the effects of sodium tripolyphosphate (STPP) on the selective flocculation of diasporic-bauxite in the presence of Ca²⁺ and Mg²⁺ ions. It was found that STPP can mitigate the detrimental effects of Ca²⁺ and Mg²⁺ ions on the dispersion of diaspore and kaolinite. When separating bauxite from the mixtures of minerals and in the presence of Ca²⁺ ions, STPP can serve as better dispersant than sodium carbonate. By jointly using STPP as a dispersant and PAAS as a flocculant, a flocculation concentrate with the mass ratio of Al₂O₃/SiO₂ (Al/Si) of 7.14 and Al₂O₃ recovery of 89.97% was produced from the feed (Al₂O₃/SiO₂ = 5.64) in the presence of Ca²⁺ ions. In contrast, with using sodium carbonate as the dispersant and PAAS as the flocculant, selectivity of the flocculation separation of diasporic-bauxite was deteriorated. These experimental data were satisfactorily interpreted by some chemical reactions occurring in the pulp, which were deduced from measured zeta potentials of the reaction resultant products and residual Ca²⁺ concentrations of the pulp.     

The reduction of nickel from low-grade nickel laterite ore using a solid-state deoxidisation method

The reduction of nickel from low-grade nickel laterite ore using a solid-state deoxidisation method was studied. The effects of temperature, time, reductant type and CaO content on the conversion percentage of the total nickel to metallic nickel (α_Ni) in the nickel laterite ore reduction process were investigated. The results showed that α_Ni was strongly influenced by the reaction temperature in both gas–solid and solid–solid reduction processes, and a higher temperature was more favourable for nickel reduction. Because the reduction mechanism of nickel laterite ore (NiO + CO → CO₂ + Ni) is indirect, a higher α_Ni (>80%) can be obtained by increasing the CO and anthracite content. In the gas–solid reduction process, a longer reaction time favoured nickel reduction, and the conversion percentage decreased when a gaseous reductant was used at 850 °C because of phase transformation. In the solid–solid reduction process, the conversion percentage of the total nickel to metallic nickel first increased and then decreased with increasing reduction time and CaO content. In both reduction processes, taenite was found by XRD in the reduced ore because of iron oxide reduction and metallic nickel formation. SEM revealed that the nickel laterite ore was transformed from large granular and sandwich structures to small granular and flocculent structures during the reduction process.     

硫化钠对硅镁型红土镍矿气基还原焙烧的影响

镍是一种重要的战略金属,随着优质硫化镍矿日益匮乏,资源丰富的红土镍矿成为重要的提镍原料。本文以红土镍矿为研究对象,甲烷为还原剂,硫化钠为添加剂,考察了还原温度、甲烷浓度、还原时间及添加剂用量对镍、铁金属化率的影响,并通过扫描电子显微镜与能量色散光谱(SEM-EDS)分析对还原产物中镍铁的聚集情况进行了研究。结果表明：在还原温度900℃、还原时间60min、甲烷浓度20％、硫化钠添加量10％的条件下,还原产物中的镍、铁金属化率可分别达到89.05％、5.10％。硫化钠的加入促进了镍铁颗粒的聚集长大,有利于镍铁颗粒与杂质的分离,同时生成的FeS抑制了铁的深度还原,实现了镍的选择性还原。     

酸浸法从低品位氧化锌矿及含锌废石制备碱式碳酸锌

采用酸浸法从新疆紫金低品位氧化锌矿及含锌废石制备碱式碳酸锌。在磨矿细度为-74μm占30%,液固比2,硫酸用量52kg/t矿,浸出时间2h,终点pH 1.5~2.0,锌浸出率为63%,氧化锌浸出率97%左右;浸出液采用碳酸钙预中和—碳酸钠沉锌工艺回收锌,在预中和终点pH 4.5~5.0、碳酸钠沉锌终点pH 8.0左右,最终获得锌沉淀率为99%,锌品位约50%的碱式碳酸锌产品,该产品可作为生产电锌的原料。