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.     

The influence of phyllosilicate mineralogy on the rheology of mineral slurries

Phyllosilicate minerals have been shown to present some rheological challenges during ore beneficiation, with difficulties such as reduced flotation rates and complex tailings treatment arising. This study focuses on two phyllosilicate minerals which commonly exist as major gangue components in many industrial ores: muscovite with its thin platy structure and vermiculite which exhibits concertina-like swelling behaviour.The surface charge distribution of the minerals is evaluated using electrokinetic zeta potential measurements and potentiometric titrations. Rheology tests give the plastic viscosities and Bingham yield stresses of the suspensions. The results show that muscovite and vermiculite particles have an apparent negative charge due to the high aspect ratio of the negatively charged tetrahedral faces to the edges within a tetrahedral-octahedral-tetrahedral (T-O-T) layer configuration. The charge separation between the edges and faces results in the non-typical stacking behaviour of muscovite and vermiculite particles, forming suspensions with higher Bingham yield stresses than quartz, a non-phyllosilicate isotropic mineral with a regular non-platy morphology. However, upon yielding, these structures are destroyed and the resultant suspensions are characterised by low Bingham viscosities similar to isotropic minerals.This study provides a preliminary understanding of the flow behaviour of muscovite and vermiculite.     

A preliminary rheological classification of phyllosilicate group minerals

With the increased exposure to progressively complex ores, there is growing concern over the effects of phyllosilicate gangue minerals. These minerals present challenges during ore beneficiation, with issues such as reduced flotation performance and complex tailings treatment arising. Often broadly classified as ‘clays’, the understanding of the distinct behaviour of phyllosilicates remains poor. This work focusses on talc, illite and kaolinite, and forms part of an ongoing study which aims at investigating the entire phyllosilicate group, categorised as serpentine, micas; talc/pyrophillite, kaolinites, illites, smectites and vermiculite. Using pure minerals belonging to each phyllosilicate type, a comprehensive surface charge and rheological analysis was conducted, incorporating their charge anisotropy and non-spherical morphology. The mineralogy was discussed, based on pre-existing knowledge of the minerals. Talc, kaolinite and illite suspensions are characterised by high yield stresses and low viscosities, with differences in their behaviour attributed to variations in charge anisotropy, aspect ratio and surface morphology. A comparison with other phyllosilicates showed that muscovite (mica) results in the least rheologically complex suspensions, while the fibrous nature of chrysotile (serpentine) leads to suspensions with the highest yield stresses and viscosities. The other minerals demonstrate intermediate rheological behaviour. Such a classification may be foundational to geometallurgical advances which can enable process performance predictions based on mineralogy.     

Rheological behaviour of lateritic smectite ore slurries

The characterisation and rheology of several nickel laterite smectite ores and pure minerals are compared to assess the effect of mineralogy and particle size on the viscosity of high pulp density slurries. A vane viscometer was used to determine the “optimum pulp density” (OPD) that gave a yield stress of 100 Pa which is considered to be optimal for pumping slurries into autoclaves in the HPAL process. In general, slurries containing finer particles were more viscous and smectite slurries exhibited poor rheological behaviour as compared to slurries of goethite < kaolin < talc < hematite < maghemite < magnesite. Blending the smectite ores with a fraction of the pure minerals improved the rheological behaviour of the pulp and can increase the optimum pulp density of the smectite blend by over 5% w/w.When the physical properties of the smectite ore and slurry were examined, a very good linear correlation was obtained between the optimum pulp density and the settling density which provides a simple measure of predicting rheological behaviour of slurries. The variation in the viscosity of the nickel laterite ores depends largely on their mineralogy and particle size distribution. The mean particle size and P₈₀ values of various smectite ores containing the same mineral phases were also found to have a reasonably good linear correlation with OPD in saline water, but the correlation of ore surface area with OPD was a poorer fit.     

The point of zero charge of monazite and xenotime

The point of zero charge (PZC) for monazite and xenotime reported in the literature has a wide range. Chemical modelling from this study shows that variation in the chemical composition of the monazite and xenotime samples can have detrimental effects on the chemical speciation of the mineral surfaces. It has been found that any slight variation of the chemical composition of the mineral surface would, therefore, cause a reversal of surface charge. This explains the wide variation of PZC of different rare earth mineral samples from different mines.     

Reductive dissolution of ferric iron minerals: A new approach for bio-processing nickel laterites

Nickel laterites represent the major ore reserves of this base metal present in the lithosphere. However, processing these ores by conventional technologies involves considerable energy or reagent expenditure and consequently is less cost-effective than extracting nickel from sulfide ores. Biological options, using metal-complexing organic acids and mineral acids generated by fungi and bacteria, have been investigated but generally found to be ineffective in terms of extraction dynamics or yields. We have examined the possibility of using bacteria that can bring about the reductive dissolution of ferric iron minerals and thereby facilitate the extraction of nickel from a lateritic ore at relatively low (<30-45 °C) temperatures.Four species of iron-reducing acidophilic bacteria were screened for their abilities to solubilise nickel from a limonitic laterite ore in which the major iron mineral present was goethite. One of these (Acidithiobacillus ferrooxidans) was selected for further study only the basis of it being able to use a cost-effective energy source (elemental sulfur) to mediate the dissolution of goethite at mildly acidic conditions (pH < 2). Cultures were set up in 2 L bioreactors, maintained at pH 1.8 (±0.1) and 30 °C, and initially aerated (to promote growth of the bacteria on sulfur) and then switched to anaerobic conditions when nickel laterite ore (crushed to <6 mm, with a nickel grade of 0.5%) was added. Over 70% of the nickel present in the ore was solubilised within 14 days, and solubilised metals remained in solution due to the low pH of the leachate. In contrast, only 10% of the nickel was solubilised (by non-reductive acid dissolution) when the cultures were continuously aerated. The results suggest that biological processing of limonitic nickel laterites is technically feasible and, more generically, that reductive dissolution can be used to bioprocess ferric oxide mineral ores.     

六偏磷酸钠在磷矿浮选中的应用及作用机理

磷矿石是磷化工生产的重要原料,在国民经济的发展中占有重要地位。磷矿石入选品位的降低、有用矿物与脉石矿物性质相似、矿物嵌布粒度过细等不利因素影响着磷矿选矿技术的发展。通过研究药剂与矿物之间的相互作用机理有助于改善矿物的选别效果,综述了磷矿石的重要性和浮选现状,着重研究了六偏磷酸钠在中低品位磷矿石浮选中的应用及作用机理。研究发现六偏磷酸钠在磷矿石浮选中有两个主要作用:一是六偏磷酸钠的加入会与捕收剂在磷灰石矿物表面形成竞争吸附,抑制捕收剂在磷灰石矿物表面的吸附,从而改变矿物的亲疏水性;二是六偏磷酸钠的加入会引起矿物表面电荷发生改变,使得矿物颗粒间相互作用力随之发生改变,增加矿物颗粒的分散性,从而优化矿物浮选条件。      

以多视角研究评价温石棉的安全性

纤维物质的安全性是指健康与安全、交通制动与安全、泄漏与安全、节能与可持续发展安全等系列范畴的全方位安全观。本文综合论述了纤维物质在生物蓄积性与毒性实验、生物活性与界面效应、有关致癌问题的研究进展、纤维物质安全性评价准则与研究视野。建议从纤维物质可能致病导因和发病机理两个端区链接进行跨学科、多产业的联合研究,以制订行之有效的安全性评价准则和安全使用法规。     

The influence of particle shape properties and associated surface chemistry on the flotation kinetics of chalcopyrite

The role of particle shape properties in determining flotation kinetics was investigated in this study. −150/+75 μm chalcopyrite was floated in a microflotation cell, and shape properties of the timed concentrates were quantified using a mineral liberation analyser - a mineralogical characterisation system based on automated scanning electron microscopy. It was found that, when floated in the absence of collector, particles with angular shape features reported to the concentrate faster than round particles. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) showed that angular particles also exhibited surface chemistry characteristics favourable for flotation. When particle floatabilities were high (i.e. when floated in the presence of potassium amyl xanthate), shape properties were not found to contribute significantly to the rates at which particles floated.     

Influence of sodium thiosulphate on oxidation of sulphide minerals during selective flotation of copper-nickel ores

The studies of sulphur distribution in oxidation products of pyrrhotite and chalcopyrite being components of Cu-Ni ores showed that the elementary sulphur — sulphoxide ion ratio on the mineral surface and in the liquid phase of mineral suspensions changes in the presence of sodium thiosulphate. Sodium thiosulphate exhibits properties of a reducing agent and prevents formation of hydrophobic elementary sulphur on pyrrhotite surface due to oxygen absorption and oxidation of thiosulphate-ions to sulphates. The decrease in pyrrhotite floatability is observed, and more favorable conditions are provided for selective flotation of chalcopyrite on copper-nickel ore processing. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 89–94, July–August, 2006.     

碳酸根和硫酸根对蛇纹石和黄铜矿矿浆流变性和浮选的影响

从矿浆流变学的角度出发,通过对矿浆流变性测量及矿物浮选试验,考察在不同碳酸根和硫酸根浓度下矿浆流变性与矿物浮选速率的变化规律。结果表明：碳酸根和硫酸根随浓度的增加都能显著降低矿浆表观黏度和屈服应力值,对矿物颗粒起分散作用。碳酸根和硫酸根的加入对黄铜矿和蛇纹石的浮选回收均有一定的促进作用,但主要是通过加快黄铜矿的浮选速率,降低精矿中MgO含量,从而达到相对抑制蛇纹石的效果。蛇纹石浮选速率与矿浆黏度间呈一定的负相关关系。     

A rheological investigation of the behaviour of two Southern African platinum ores

With the installation of ultrafine grinding on many platinum operations in southern Africa, there were concerns as to whether this would cause rheologically complex behaviour during the subsequent flotation of the ore. Rheologically complex behaviour refers to the non-Newtonian behaviour experienced by some suspensions, associated with exponential increases in yield stress and viscosity with increasing solids content. This is attributed to particle size and solids concentration effects, surface chemistry, and mineralogy. In this study, the rheological behaviour of two different platinum ores; a western limb UG2 ore and a Great Dyke platinum ore were investigated and compared with that of single mineral studies of the major gangue minerals of platinum ores (chromite, orthopyroxene, plagioclase and talc). The results show that Great Dyke ore is considerably more rheologically complex than UG2 ore. Great Dyke flotation concentrate shows high yield stress and viscosity at low solids concentrations (>20 vol.% solids). Should the ROM ore in a Great Dyke flotation operation suddenly show significant changes in ore mineralogy, the rheological properties of the slurry should be considered since they may be detrimental to the overall performance of the operation (e.g. loss of recovery through poor gas dispersion). In contrast, the rheological behaviour of UG2 flotation samples shows little cause for concern for the plant operator. Comparison of the pure mineral samples shows that the complex rheological behaviour of the Great Dyke ore may be attributed to the high degree of low temperature alteration and the formation of phyllosilicate minerals such as talc, more than particle size effects.     

Electrokinetic behavior and flotation of kaolinite in CTAB solution

The electrokinetics and flotation behavior of kaolinite in cetyltrimethylammonium bromide (CTAB) solution were studied. The point of zero charge (PZC) of kaolinite is 4.3. The possible mode of CTAB adsorption on kaolinite is due to Coulombic and Van der Waals forces revealed by zeta-potential and FTIR measurements. The negative zeta potential of kaolinite and the adsorption of cationic collectors on kaolinite were higher in alkaline media than in acidic media. However, the flotation tests show that the kaolinite exhibited much better floatability in the acid range than in the basic pH range in the 2 × 10⁻⁴ M CTAB solution. The surface charge of the basal plane is negative and that of the edge is positive in the acid pH range. The aggregation occurs possibly by electrostatic interaction between particles because of different charged based plane and edges, and makes floatability of kaolinite better in an acid pH range.     

Rheological investigations of sulphide mineral slurries

The flotation separation of ultrafine (−5 μm) sulphide mineral particles is inherently problematic, since even strongly hydrophobic fines have relatively low flotation rate constants. Selective aggregation of fines provides a route for enhanced flotation selectivity, but requires detailed knowledge and ultimately control of the electrostatic and hydrophobic inter-particle forces acting in concentrated sulphide mineral slurries. Rheological investigations offer insight into these inter-particle interactions. Rheological studies of ultrafine sphalerite particle slurries at pulp densities akin to those experienced in flotation practice were undertaken; the influence of pH, electrolyte concentration, activating copper (II) ions and ethyl xanthate ions on the level of pulp aggregation, as defined by the yield values and viscosities, are reported.The rheological behaviour of oxidised, and effectively hydrophillic, sphalerite particles (in the pH range 4 to 10) are controlled by electrostatic repulsive forces and yield values scale inversely with electrophoretic mobilities. Copper (II) activation, ethyl xanthate treatment and addition of slime particles dramatically affect pulp rheology and, depending on the particular concentrations and conditions employed, cause either aggregation or dispersion of the pulp. We show that an understanding of the theological behaviour of sulphide mineral pulps enhance our knowledge of particle-particle (and bubble-particle interactions) and may enable fine particle flotation performance to be optimised.     

On the mechanism of the flotation of oxides and silicates

The mechanism of flotation of oxide and silicate minerals was established long ago as being due to the electrostatic attraction between the charged surface and the charge of the collector. What is less well established is the mechanism of the charging of the mineral surface. Most researchers have postulated that the adsorption of H⁺ is the cause. However, the adsorption model and its derivatives (such as the amphoteric and multisite-adsorption models), do not successfully describe the data for the zeta potential as a function of pH. In particular, these adsorption models have the following features that are not observed: (i) they are symmetrical about the point of zero charge, whereas the data is asymmetrical, (ii) they have an inflection at the pK_a values, leading to an asymptotic approach to the point of zero charge, whereas such an inflection is not observed, and (iii) they only fit the data in its extremes, that is, when the pK_a values differ by orders of magnitude, or are very close to one another. An alternative mechanism of charging is proposed here that is based on the dissolution of ions from and deposition of ions onto the mineral surface. It is shown that this model (a) fits the data, (b) is consistent with the thermodynamic model for reversible interfaces, (c) is consistent with the thermodynamics of the overall reaction and its solubility, (d) indicates reasons for the ageing of surfaces and (e) displays the observed features of zeta potential measurements as a function of pH, that is, it is pseudo-Nernstian and asymmetrical in nature. Application of the proposed theory is discussed for the flotation of quartz and corundum.     

氧化锌矿物的表面性质与浮选关系研究综述

氧化锌矿石结构和共伴生关系复杂,表面性质相似,浮选分离难度较大。氧化锌矿中有用矿物异极矿或菱锌矿在浮选过程中难以与含钙脉石矿物方解石和白云石有效分离。因此,对异极矿、菱锌矿及其含钙脉石矿物的表面性质以及其与浮选行为之间的关系进行深入分析可为其高效浮选分离提供理论基础。系统介绍了异极矿和菱锌矿及其含钙脉石矿物表面性质的研究现状,主要包括矿物的表面断裂键、表面润湿性、表面能、表面电性、表面溶解性等,并评述了矿物表面性质与浮选之间的关系。其中,表面断裂键决定矿物暴露面的活性位点;表面润湿性决定矿物天然疏水性;表面能与矿物吸附药剂能力有关,吸附能越负,药剂与矿物表面的相互作用越剧烈;在浮选过程中,带与矿物表面相反的电荷的捕收剂容易通过物理吸附导致浮选;有用矿物表面溶解的金属离子会活化脉石矿物,导致浮选分离困难。最后,对氧化锌矿物表面性质的未来研究方向进行了展望。     

Electrokinetic and flotation behaviors of hemimorphite in the presence of sodium oleate

The electrokinetic and flotation behaviors of hemimorphite in sodium oleate solution were studied. The results of micro-flotation experiments indicate that hemimorphite shows good floatability at pH 4.0–9.0 and pH 11.0. The point of zero charge (PZC) of hemimorphite is pH 5.1. Zeta-potential and FTIR measurements indicate that the mechanism of sodium oleate adsorption on hemimorphite involves both chemical and physical interactions. Sodium oleate mainly reacts with the Zn on the hemimorphite surface. In acid/base pH range, the aggregation among hemimorphite particles which is more likely caused by hydrophobic interaction than electrostatic interaction improves hemimorphite’s floatability.     

Decoupling rehology and slime coatings effect on the natural flotability of chalcopyrite in a clay-rich flotation pulp

Clay minerals are a commonly occurring gangue in mineral beneficiation operations and occur in a variety of ore deposits, including porphyry copper ores. The presence of clays in mineral beneficiation circuits can cause a wide range of different problems, including that of slime coatings on valuable minerals and elevated viscosities of flotation pulps. The aim of this work was to decouple and estimate the relative magnitudes of the slime coatings and pulp rheology effects on the natural floatability of chalcopyrite in a model mineral system. It was found that the two phenomena can be partially isolated and that they both have a detrimental effect on flotation performance. It was also found that the level to which these two phenomena affect chalcopyrite recovery is of a similar order of magnitude.     

A new industrial mineral: Huntite and its recovery

Huntite is a new industrial mineral. The industrial utilization of huntite is not well known. Huntite formations include different types of minerals such as hydromagnesite, magnesite, clay minerals, aragonite and dolomite. Separation properties of these ores have not exactly been determined yet.In this study, characterization of huntite ores was made and separation conditions for huntite from the associated mineral, magnesite were investigated. The effect of modifying reagents like sodium silicate and carboxymethyl cellulose on surface properties of huntite were also examined. Electrokinetic measurements showed that the surface charge of huntite becomes positive in the presence of MgCl₂ and CaCl₂. On the other hand, carboxymethyl cellulose was found to be a strong depressing agent for huntite in the alkaline region. The result of flotation tests performed with run of mine ore sample, huntite concentrates were produced with 97–98% huntite contents and 76–86% recoveries.