Ligand-promoted dissolution of serpentine in ultramafic nickel ores

The ligands catechol, citrate, EDTA, oxalate and tiron were investigated for their ability to improve the dissolution of serpentine in ultramafic nickel ores at neutral to alkaline pH to enhance mineral carbon sequestration. It is desirable to leach magnesium from serpentine in ores at neutral to alkaline pH so that leaching and carbonation can be conducted at the same pH value, and ultimately so that the reagent requirements of mineral carbon sequestration can be reduced. Both solution modeling and experimental work were conducted. The solution modeling revealed that each of the ligands studied is able to enhance the solubility of magnesium at the desired pH, with the order of effectiveness being EDTA > tiron > citrate > catechol > oxalate. Experimentally it was shown that the ligands studied could improve both the total amount and rate of magnesium leaching from ultramafic nickel ores. The order of ligand effectiveness based on the experimental work for the Pipe ore was EDTA ⩾ tiron > catechol > oxalate ⩾ citrate. For the OK ore, the order was tiron > EDTA = catechol > oxalate > citrate. Overall, the ligands studied in this work, particularly EDTA, tiron, and catechol, appear promising for enhancing the dissolution of serpentine in ultramafic nickel ores at neutral to alkaline pH.     

Mineral carbon storage in pre-treated ultramafic ores

Mineral carbon sequestration (MCS) is a type of carbon storage based on natural rock weathering processes where CO₂, dissolved in rainwater, reacts with alkaline minerals to form solid carbonates. Although MCS has advantages over other carbon storage techniques, an economic MCS process has not yet been developed. Two approaches were taken in this work to attempt to reduce the cost of MCS. The first approach was to use a waste material, serpentine waste from ultramafic nickel ore processing, as a feedstock. The second approach was to develop pre-treatments to increase the carbon storage capacity of the feedstock. Two pre-treatments were investigated in this work, including microwave pre-treatment and leaching with ligands at neutral to alkaline pH. The carbon uptake of ultramafic ores was found to increase with increasing microwave pre-treatment after a threshold heating time of 4 min was surpassed. A maximum carbon uptake of 18.3 g CO₂/100 g ore (corresponding to a carbonate conversion of 36.6%) was observed for microwave pre-treated ore. The increase in carbon uptake was attributed primarily to the conversion of serpentine to olivine in ultramafic ores that occurs as result of microwave pre-treatment. The effect of five different ligands (catechol, citrate, EDTA, oxalate and tiron) on the carbon uptake of ultramafic ores was investigated. Of the ligands tested, only catechol and tiron were found to both improve the leaching of magnesium from the ores and the quantity of CO₂ stored. A maximum carbon uptake of 9.7 g/100 g ore (corresponding to a carbonate conversion of 19.3%) was observed for ultramafic ore pre-leached and carbonated in tiron solution at pH 10. This is the first time ligands have been reported to improve the carbon uptake of mineral carbon sequestration feedstock. Although process optimization work was not conducted, both microwave pre-treatment and leaching with ligands at neutral to alkaline pH show promise as ways to lower the cost of MCS.     

Effect of microwave pre-treatment on ultramafic nickel ore slurry rheology

Low-grade ultramafic nickel ores, while representing a large potential nickel resource, are difficult to process due to their high serpentine content. Serpentine is anisotropic and the mineral particles tend to be non-spherical, resulting in challenging slurry rheology. In general, suspensions of serpentine minerals have high viscosity and yield stress, which can be detrimental in comminution and flotation operations. It is proposed that ultramafic nickel ores be treated with microwave radiation prior to grinding in order to reduce slurry viscosity and yield stress. The rheology of two different ultramafic nickel ores, before and after microwave pre-treatment, was characterized in this work. Serpentine minerals were found to dominate the rheology of the untreated ultramafic nickel ores, with the ore containing minor chrysotile exhibiting higher viscosity and yield stress than the ore containing strictly lizardite serpentine. Microwave pre-treatment was found to greatly reduce the shear viscosity (average 80% reduction at 200 s⁻¹) and direct yield stress (peak yield stress reduced by 92–93%) of ultramafic nickel ore slurries. The reduction in slurry viscosity and yield stress of the ore slurries as a result of microwave pre-treatment was attributed to the conversion of serpentine to olivine.     

Statistical validation of standardless and standard-based analysis by X-ray fluorescence spectrometry in iron ores characterisation

An X-ray fluorescence (XRF) study comparing the performances of standardless or semiquantitative analysis in relation to the traditional standard-based or quantitative analysis technique is presented. This comparison using precision lines and simultaneous confidence intervals provides reliable information about the precision and trueness that each technique can achieve. This study enables the comparison of the results obtained with two different analytical approaches for iron ore samples in terms of precision and accuracy of results, sample preparation and availability of standards. A new technique for assessing the accuracy of an analytical method using linear regression is presented, wherein the results of both analyses are regressed against certified reference materials. The statistical test performed is based on the joint confidence interval for the slope and the intercept of the regression line calculated considering the uncertainties in both axes or in both analytical methods. The slope, intercept and variances associated with the regression coefficients are calculated with bivariate least-squares regression. Some chosen standard-samples were analysed for statistical validation of the methods. These samples had sufficient replicates to perform the calculations and later statistical comparison between the accuracy (precision and trueness) of each analytical method and evaluation of its precision lines.     

Mixed sulphide-oxide lead and zinc ores: Problems and solutions

Mixed sulphide-oxide lead and zinc ores are most often found in the transition, and occasionally in the oxidised, zones of lead-zinc ore-bodies. They are of great importance because there are numerous unexploited or abandoned reserves of these ores in the world.However they present difficulties for conventional mineral processing due to complex mineralogy. In this paper, the specific problems associated with these types of ores are described and methods for solving these problems, combining economic and technical considerations, are discussed.The results of experiments carried out at laboratory scale are presented, in which the dissolution of mixed ore in sulphuric acid without oxidising agents was investigated. The results show the feasibility of zinc recovery from mixed sulphide-oxide lead and zinc ores, which underlines the potential of this approach. We also propose a conceptual flow diagram for the hydrometallurgical processing of these ores.     

硅镁型红土镍矿脱羟基相变过程动力学研究

镍具有优良的物理化学性质,应用领域广泛,镍资源主要存在于硫化镍矿和红土镍矿中,目前红土镍矿正逐渐成为主要的镍提取原料,由于红土镍矿含水量大,在冶炼过程中通常要对矿石进行高温预处理,目的是为了去除矿石晶格里的羟基水以及预先还原部分金属,但这部分羟基水的脱除需要消耗大量能量,并且产生物相变化,对预还原及浸出都会产生影响,因此探究红土镍矿脱羟基过程的物相变化及动力学条件对后续加工作业具有重要的研究意义。本文利用热力学分析软件模拟计算了红土镍矿加热过程中可能发生的化学反应,并采用热重-差热分析及 XRD 分析研究了硅镁型红土镍矿加热过程的物相变化,从室温到1400°C范围内进行了5种升温速率的非等温动力学实验,在256.8°C、582.8°C和823.0°C 处有三个特征峰,分别对应褐铁矿脱羟基、蛇纹石脱羟基以及硅酸盐矿物的相变。采用非等温动力学模型求解来确定反应的表观活化能及指前因子,使用Flynn-Wall-Ozawa 法和Kissinger-Akahira-Sunose 法计算了蛇纹石脱羟基过程的活化能,并利用Satava-Sestak法对常用的30种机理函数进行拟合,保留符合条件的机理函数,确定 Avrami-Erofeev 方程的A1/3函数符合脱羟基过程,其积分形式为G(α)= [-ln(1-α)]3,求得蛇纹石脱羟基反应的活化能为258.71 kJ·mol-1, lnA为28.94 S-1,平均线性相关系数为 0.9951,蛇纹石脱羟基过程符合随机成核及随后生长模型。     

微波技术在选矿中的应用

介绍了微波加热的原理和所具有的即时性、整体性、选择性、高效性、无污染等特性,从碎矿、磨矿、浮选、磁选、浸出、矿石预处理等方面对微波技术在选矿中的应用情况进行了综述,指出微波技术在选矿领域中的应用有着广阔前景。     

The effects of mineralogy on the biological leaching of nickel laterite ores

The amenability of limonite ore, the iron rich nickel laterite phase, was observed to be less than saprolite, the silicate rich phase, when subjected to biological leaching with heterotrophic microorganisms. To understand this difference, controlled leaching of the various nickel laterite minerals was conducted using citric acid to mimic the chemical action of the organisms and subsequent characterisation of the leached residues. The raw ore and the leached mineral residues were examined using high-resolution synchrotron based X-ray diffraction and optical microscopy. The possible contribution of electrosorption and solid porosity was also considered. The results suggest that although electrosorption contributes to nickel and cobalt losses, it is the structural changes induced by the acid in the minerals which effects the recovery of the metals. Citric acid was found to dehydroxylate saprolite minerals resulting in an unstable nickel oxide and thus making it susceptible to acid attack. This behaviour was not observed in the limonite ore, which was found to be poorly leached by citric acid.     

A detailed mineralogical assessment of sphalerites from the Gamsberg zinc deposit, South Africa: The manganese conundrum

The Gamsberg zinc deposit, located in the Northern Cape Province, represents South Africa’s greatest and most important unexploited base metal resource. Yet, in spite of its size, the low zinc grade combined with the high manganese content of the sphalerite continues to prohibit development of the deposit, as the high manganese content makes the zinc concentrates unsuitable for processing by conventional smelting methods, i.e. roasting, leaching/solvent extraction and/or electrowinning.Although numerous published investigations of the Gamsberg deposit have been undertaken, few have focused on the correlation between petrography and mineral chemistry of sphalerite and their implications on mineral processing. In accordance, the aims of this investigation are to highlight the importance of conducting a detailed geometallurgical investigation, as well as provide some new constraints on the metallurgical behavior of sphalerite and zinc concentrates from the Gamsberg deposit. Detailed analysis of sphalerite by petrographic and various microanalytical techniques reveal a marked absence of correlation between crystal morphology and mineral chemistry, necessitating a chemically based classification scheme. As such, six sphalerite populations where identified. They are: zinc-, cobalt-, iron- and manganese-rich, as well as manganese-enriched and manganese-poor. The zinc- and cobalt-rich populations display high zinc contents and low concentrations of iron and manganese, while the iron-rich population displays higher iron contents. Dominating the sphalerites of the mineralized pelitic schist is the manganese-enriched population. Of volumetrically lesser importance are the manganese-poor and -rich populations. The manganese-rich population contains high levels of iron, manganese, cobalt and cadmium relative to the zinc-rich population. In contrast, the manganese-poor population displays similar concentrations of cobalt and cadmium to the zinc-rich population, with iron and manganese intermediate between the zinc- and iron-rich populations.Comparisons between the sphalerite populations and milling size fractions reveal a consistent correlation between sphalerite mineral chemistry and size fractions with the coarser-grained concentrates being economically less favorable compared to the finer-grained concentrates, which display higher zinc contents. Combined with other lines of evidence, this suggests that the sphalerites of mineralized pelitic schist exhibit extensive solid solution that will have an effect on process optimization. For instance, it suggests that milling to a finer grain size will not remove or reduce the iron and manganese content. Another concern to processing will be the variable mineral chemistry of sphalerite, which might cause some sphalerites to display a delayed response during flotation or misreport to the lead concentrate. In spite of this, using solvent extraction, the elevated manganese content of the concentrates could be controlled, while simultaneously recovering zinc and manganese for sale. Hence, the recovery of manganese metal as a by-product could potentially enhance the economics of the deposit. Alternatively, other forms of mineral processing and metal extraction must be evaluated to meet the target grades and recoveries.     

The effect of acrylamide-co-vinylpyrrolidinone copolymer on the depression of talc in mixed nickel mineral flotation

Copolymers of acrylamide and vinylpyrrolidinone with varying compositions have been synthesised and employed to depress talc in a model flotation system with process plant operation conditions. Adsorption isotherms indicated that the hydrophilic acrylamide homopolymer has a very low affinity for the hydrophobic talc surface, whereas vinylpyrrolidinone homopolymer strongly adsorbs onto the talc surface. Micro-flotation experiments revealed that the copolymer system can induce stronger talc depression than the homopolymer variants, with the most effective copolymer depressant having 25-30% vinylpyrrolidinone incorporation. The copolymer system is observed to have inherited the strong talc affinity of vinylpyrrolidinone polymer and the strong hydrophilic property from polyacrylamide. This combined effect facilitates the desired strong talc depression in single mineral flotation. However, this copolymer system has similar adsorption affinity on both the talc and pentlandite, hence depressing both talc and pentlandite in the mixed mineral flotation system. This research shows that a sufficient hydrophobic balance on the polymer is necessary for the adsorption and subsequent depression for talc. However, polymer with high adsorption selectivity is required to be a successful synthetic talc depressant for mixed mineral system.     

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.     

Microwave heating of gold ores for enhanced grindability and cyanide amenability

In leaching processes, the mass transport of lixiviants from the bulk of the solution to the site of the mineral of interest is usually the slowest step. Diffusion becomes slower when the particles to be leached are occluded in host minerals. Access to the mineral of interest is enhanced by micro-crack formation within the host minerals as it enhances percolation and migration of lixiviants. Micro-crack formation also augments grinding and allows size reduction and liberation at a lower stress level. In this research, microwave pretreatment was used to augment the grinding of a free-milling gold ore containing quartz, silicates and iron oxides. Under microwave irradiation, selective heating of the different mineral components resulted in thermal stress cracking. Microwave processing enhanced the grindability of the ore, and crushing strength was reduced by 31.2%. The presence of micro-cracks improved leaching rate, and over 95% extraction was achieved within 12 h as against 22 h for the non-microwaved sample. Such a strategy can be used to maximize recovery and man-hours on processing plants.     

微波消解-氢化物发生原子吸收法测定进口铁矿中的砷

采用（盐酸+硝酸+氢氟酸）微波消解溶解进口铁矿,然后利用氢化物发生原子吸收法测定样品中的砷。本方法检出限低、线性范围宽,能够满足铁矿石的分析要求。     

The efficiency of indigenous and designed consortia in bioleaching stirred tank reactors

The efficiency of bioleaching is dependant on the establishment of an active microbial community. There is debate as to whether an indigenous microbial community is superior to one composed of microbial strains selected for specific physiological traits. The bioleaching efficiency of three microbial communities was studied: the indigenous community of a commercial bioleaching system (KCCL), a reconstituted consortium of the four major organisms which comprise KCCL that had been ‘un-adapted’ through a period of continuous maintenance in synthetic media (KCCR) and a specifically designed consortium of bioleaching organisms (KCCD). Acidithiobacillus caldus was unable to re-establish itself in the reconstituted, un-adapted consortium. However, the bioleaching rate of this consortium improved over time, and its overall performance was very similar to that of the indigenous community. This was despite the absence of an obligate sulfur-oxidising species, which resulted in the generation of substantially less acid. The performance of the designed consortium was poor, and the results implied that bioleaching consortia (mesophiles or moderate thermophiles) cannot be assembled ‘off-the-shelf’, at least not without a substantial period of adaptation.     

难选氧化铜矿石的选矿方法及研究方向

这是一篇矿物加工工程领域的论文。新疆某铜矿石中矿物组成复杂、属于复杂难选氧化铜矿。矿石中硫化铜占总铜的35.67%,游离氧化铜和结合氧化铜占总铜的64.33%。脉石矿物种类多且与目标矿物之间嵌布关系复杂。采用先浮硫化铜矿物,再浮氧化铜矿物的原则流程进行了选矿工艺技术条件研究。针对该矿石性质,开展浮选条件实验,获得较佳工艺参数,磨矿细度-0.074 mm 65%,石灰用量为2500 g/t、捕收剂Z-200用量为100 g/t、硫化钠用量为1750 g/t、硫酸铵用量为550 g/t、戊基钠黄药用量为160 g/t。在较佳磨矿细度和药剂用量下,开展闭路浮选实验,闭路流程可以获得硫化铜精矿和氧化铜精矿两种产品,其混合铜精矿中Cu的品位为25.59%,Ag的品位为507.27 g/t,铜回收率为73.07%,银总回收率为70.27%。本研究为该氧化铜矿资源的高效利用提供了技术支撑。     

Influence of mineralogy and ore texture on pentlandite flotation at the Nkomati nickel mine,South Africa

The influence of ore mineralogy and ore texture on flotation response was studied for 29 samples from the main mineralised zone at Pit 3 of the Nkomati Ni mine, through laboratory scale flotation testing, laboratory assay, and mineral liberation analyser examination of the ore and the concentrates. The individual sample flotation responses vary widely in terms of Ni grade, and cumulative Ni recovery. It is demonstrated that this is a complex function of ore mineralogy and ore texture. Chalcopyrite is the first sulphide to float, followed by pentlandite and finally pyrrhotite, in ore samples with dominant chalcopyrite, or where pentlandite, pyrrhotite and chalcopyrite occur in equal abundance. However in samples with a high ratio of pyrrhotite to pentlandite and chalcopyrite, pyrrhotite floats earlier than expected, reports to concentrate over the entire flotation period, and depress and extend the flotation of pentlandite over the flotation interval with no clear peak of Ni recovery during flotation. Primary silicates (e.g. olivine and pyroxene) and alteration-related minerals (talc, tremolite and chlorite) are naturally floating, and hence affect the flotation of pentlandite in a similar manner to that of pyrrhotite. The most problematic ore at Nkomati in terms of Ni recovery is characterised by fine disseminated and fine bleb- or net-texture sulphides, contain abundant olivine, pyroxene, amphibole, talc and tremolite, and include abundant metamorphism-related country rock xenoliths (with calc-silicate minerals such as diopside and tremolite).     

DEM validation of media shape effects on the load behaviour and power in a dry pilot mill

Simulations were carried out in Metso’s DEM simulator so as to draw up an understanding of the effects the various ways of defining media shapes within the simulator have on the load behaviour and mill power draw. Wits University made available the load behaviour and mill power draw experimental results for the spherical balls, worn balls and cylpebs so as to validate the DEM simulations. The spherical media were defined by a regular spherical shape model and a multi-faceted polyhedron model. Worn balls were defined by super quadric models. A comparison was made between spherical media shapes, non-spherical single media shapes and a distribution of non-spherical media shapes and sizes in representing a load comprised of worn balls. The effect of increasing angularity of non-spherical media shapes on mill power was investigated. The cylpebs were modelled using a regular cylindrical shape model and the effects of friction on the power drawn were determined.