The effects of chrysotile mineralogical properties on the rheology of chrysotile suspensions

Chrysotile (serpentine) is a phyllosilicate mineral that occurs as a major gangue mineral in many ores (e.g. Mt. Keith nickel sulphide ore, Western Australia). It is believed that the distinctive morphology and electrical surface charge of chrysotile particles are central to the problematic rheological behaviour and low solids throughput typically experienced in the processing of such ores. This study investigates the effects of both these factors on the rheology of chrysotile suspensions.Chrysotile particles were found to carry a net positive charge over the range pH 2-11, with an apparent point of zero charge at pH 8.23. This is a direct result of the convoluted mineral structure of chrysotile fibres, which comprise a positively charged brucite outer layer. The disparity in the point of zero charge and range of maximum yield stress for chrysotile is consistent with the anisotropic nature of chrysotile particles. The long, thin fibres are easily entangled to form suspensions with much higher plastic viscosities and Bingham yield stresses than non-fibrous particles.Although chrysotile shape and surface charge are fundamental to the rheology of chrysotile suspensions, it was found that shape plays a more significant role.     

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.     

Understanding the performance of a pilot vermiculite exfoliation system through process mineralogy

This paper reports on the application of process mineralogy to understand the experimental performance of a microwave based system for the exfoliation of vermiculite type minerals. When montmorillonite type clay structures are exposed to high intensity electric fields they expand very rapidly with the degree of expansion being directly related to the applied electric field strength. This basic understanding of the interaction of microwave fields with such materials has been used to develop a pilot scale microwave based process for the exfoliation of vermiculite. During commissioning of the system it was noted that vermiculites from different geographical sources behaved very differently in terms of the achieved expansion ratio. A systematic mineralogical evaluation of these different materials was carried out using Mineral Liberation Analysis (SEM/MLA), Thermo-gravimetric analysis and X-ray Diffraction (XRD) in order to determine the reasons for the variation in performance. Samples from vermiculite mines in Australia, Brazil, China and South Africa were studied. The mineralogy and mineral characteristics such as liberation, size and texture of the samples were quantified for each ore sample. The South African and Australian samples were found to be predominantly hydrated forms of mica. The Brazilian sample was predominantly composed of vermiculite while the Chinese sample was composed almost totally of hydrobiotite. The relationships between the form of hydration and degree of expansion were derived and it is shown that pure vermiculite exfoliates at lower field intensities than the other forms of hydrated mineral. The paper concludes with deductions obtained from the mineralogical assessments of the vermiculites, thereby elucidating the reasons for the performance observed for each feed material in the microwave exfoliation system.     

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.     

Behaviour of swelling clays versus non-swelling clays in flotation

The deleterious effects of clays on flotation performance are widely acknowledged but the mechanisms involved are not clearly established. Moreover, the concentrations beyond which clay minerals become problematic are not clearly defined. One major parameter is the difference between swelling and non-swelling clays which is evaluated in this study. The ore slurry pulp rheology and froth stability were monitored in the absence and presence of different clay minerals. It was found that swelling clays can adversely affect the flotation performance mainly via adsorbing water which changes the rheology and froth stability, reducing both flotation grade and recovery. Non-swelling clays had a lower effect on the rheology. Kaolinite increases the froth stability and reduces the flotation grade but illite showed the least effect on the flotation performance in this study. The potential mechanisms and critical concentrations are discussed.     

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.     

Effect of clay minerals on pulp rheology and the flotation of copper and gold minerals

In this study, the effect of bentonite and kaolinite minerals with low and high crystallinity on pulp rheology and the flotation of copper and gold minerals was investigated. It was found that clay minerals modified the pulp rheology depending on the type of clay minerals present. Bentonite, a 2:1 structured clay mineral increased pulp viscosity more significantly than kaolinite, a 1:1 structured clay mineral, and poorly crystallized kaolinite increased pulp viscosity more than well crystallized kaolinite. It was also found that pulp rheology modified by clay minerals was strongly correlated with copper and gold flotation. The higher pulp viscosity corresponded to the lower copper recovery. While high pulp viscosity was related to the decreased gold flotation, slightly increased pulp viscosity by clay minerals enhanced gold flotation.     

Determination of ferrosilicon medium rheology and stability

Ferrosilicon (FeSi) has a fast settling rate in dense suspension, attributed to its very high solids density, coarse particle size, more spherical particle shape and low medium viscosity. The fast-settling nature in dense suspension is a challenge to acquire reliable rheological data. A testing rig was set up to maintain a constant medium density during the rheology measurement by circulating the medium to keep FeSi particles well suspended. A rotational rheometer with a modified concentric bob-cup measuring system was incorporated in the testing rig. Taylor number (T_a) was calculated and a threshold T_a = 41.3 was used to identify the onset of unstable laminar flow owning to the Taylor vortices and turbulence formation in the measuring system. The data with T_a > 41.3 were excluded in the determination of rheological flow curves. Evaluation of the modified measuring system with Newtonian silicone oils of known viscosities confirmed that the system can produce true flow curves over the entire tested shear rate range for a stable laminar flow (T_a < 41.3). This data reduction procedure was applied to the FeSi medium rheology measurement. It demonstrates that FeSi medium exhibits a pseudoplastic trend with a yield stress. The apparent viscosities were calculated at two shear rates, 10 s⁻¹ that is assumed to be a typical shear rate in dense medium bath separators and 75 s⁻¹ for dense medium cyclones. A characteristic curve between apparent viscosity and medium density was established, which can be used in FeSi selection for dense medium separation. Medium stability was determined from the FeSi sedimentation rate measurement. It shows that medium stability was closely correlated with medium viscosity. A trade-off between stability and viscosity for optimal dense medium separation should be established.     

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.     

炼钢尘泥浆体理化性质与流变特性的研究

根据对炼钢ＯＧ系统除尘产生的尘泥浆体的试验数据，研究了粒级分布、沉降速度、最大沉降浓度和流变参数的数学模型。分析结果为，其精度达到一定的要求，可供管道输送设计应用。     

Effect of slurry rheology on gas dispersion in a pilot-scale mechanical flotation cell

This paper investigates the effect of slurry rheology on gas dispersion in a 100 l pilot-scale Batequip mechanical flotation cell. The study is conducted using Kaolin, Bindura nickel and Platreef slurries. All three ores display typical non-Newtonian rheological behaviour. The slurry yield stress and viscosity increase exponentially with solids concentration. Bubble size and gas hold-up vary from 0.60 to 1.10 mm and 2% to 15%, respectively. At low/moderate solids concentrations, bubble size and gas holdup display characteristic trends, as noted in numerous literature studies. At high solids concentrations, both bubble size and gas holdup decrease significantly, which is an unexpected finding. This is attributed to the formation of a ‘cavern’ of slurry around the impeller, due to the very high slurry yield stresses. This ‘cavern’ results in the generation of small bubbles in the impeller zone, but poor dispersion of these bubbles throughout the cell, resulting in low gas hold-ups.     

SiO2对钢渣矿相组成的影响

本文研究了在炼钢过程中添加SiO_2对钢渣矿物相组成的影响,并扫描电镜(SEM)和能谱仪(EDS)测定了矿物相的组成和电子散射图像,在此基础上讨论了矿物相的形成机理。选择CaO(45%)-MgO(18%)-SiO_2(10%)-Fe_2O_3(27%)作为渣系,用0.125%的B_2O_3作为稳定剂,研究SiO_2对钢渣矿相组成的影响,结果表明:在基础渣系中加入2%到4%的SiO_2时,C_3S相逐渐反应生成C_2S相;加入6%~12%的SiO_2时,C_2S相逐渐增多,出现CF和MF相,C_2F相逐渐减少;加入14%以上的SiO_2时,Mg开始溶入C_2S的现象,Mg O和C_2S相减少,生成C3MS2相。     

蛇纹石石棉煅烧改性研究

研究了不同煅烧温度和煅烧时间对蛇纹石石棉改性的影响。结果表明,烧失量随温度的增加而增加,当温度达到1000℃时,蛇纹石石棉改性产物仍然保持了纤维微观形态,为镁橄榄石纤维。     

Understanding the influence of HPGR on PGM flotation behavior using mineralogy

Due to the very fine grained nature and complexity of the platinum bearing ores from the Bushveld Complex in South Africa, numerous processing operations have investigated alternate comminution devices that can be used to liberate the platinum group minerals of the Merensky and UG2 ores at a coarser grind, at reduced energy consumption and increased throughput. In this study, the mineralogy and flotation performance of product from the high pressure grinding rolls (HPGR) was evaluated and compared to a conventional ball mill product with the aim of determining whether the HPGR product could be used for flotation without any further grinding. Results show that for both the Merensky and UG2 platinum ores, the HPGR product showed more fines and less coarse content compared to the ball mill product. No conclusive evidence of preferential liberation was observed for samples prepared by particle bed breakage. The best flotation results were obtained from the ball mill product. The results from this study have shown the definite need for an integrated approach for the interpretation of the results that extends beyond just measurements of valuable mineral liberation.     

The mineral phase quantification of vermiculite and interstratified clay minerals-containing ores by X-ray diffraction and Rietveld method after K cation exchange

Hydrothermal transformations and weathering are important mineralizing processes in carbonatite-related ores. But the transformation products of mafic minerals, such as the clay minerals, vermiculite and interstratified phases, preclude the use of X-ray diffraction, particularly the Rietveld method, for mineral phase quantification. After treatment with KCl, vermiculite and interstratified phases (all peaks roughly at 1.2, 1.4-1.5 and 2.4 nm) are converted to a phlogopite-like structure with d(0 0 1) = 1.0 nm, which can successfully be refined. The method was tested using three carbonatite-derived ores, with a total phlogopite-like phase content ranging from 1.2 to 32.3 wt.%. Comparison of the chemical analyses with the calculated chemical composition, based on the phase quantification and the mineral composition is in good agreement for major elements, such as Si, Fe and Al. For P results were also very good, but Ti and Nb are generally underestimated, and Ba is overestimated. Minerals with lower contents, as pyrochlore, approach the diffraction detection limit. Problems to accurately determine mineral composition for some of the phases also impacts on the reconciliation. The chemical composition of the pyrochlore group minerals changed, but not to an extent to constrain the usefulness of the technique. Cation exchange successfully extended the amenability of the Rietveld method for phase quantification.     

On-stream and quantitative mineral identification of tailing slurries using LIBS technique

Mineral flotation processes are controlled by monitoring the grade of the present minerals. The performance of flotation can be greatly optimized by online assaying of the minerals in the slurry flows. However, online and quantitative mineral identification of the slurries is challenging. The major focus of this research is about measuring mineral contents from the elemental concentrations acquired by an on-stream slurry analyzer operating based on laser-induced breakdown spectroscopy (LIBS). A multivariate statistical method called partial least squares regression is employed to perform the elemental to mineral conversion. In this work, the samples under study come from an iron concentrator where knowledge about the grade of silicates and iron-oxides are important for controlling the flotation plant. In total, the concentrations of six out of ten minerals were successfully estimated. This accomplishment provides quantitative knowledge about mineral contents from the nearly real-time assay data without any modification on the measurement setup or further instrumentation. This can lead to many benefits such as rapid control of concentrate quality, enhanced recovery and savings in money, time, energy and manpower. The proposed technique is applicable to all types of slurry samples.     

金川铜镍矿贫矿石选矿产品的工艺矿物学研究

通过对金川铜镍矿某矿区正在试产的贫矿石现场流程的精矿、尾矿样品的工艺矿物学研究发现,主要存在的问题是精矿Ni、Cu品位低,MgO含量高。其主要原因是滑石易浮,大量在精矿中富集造成的。因此,要提高铜镍品位,降低精矿中MgO的含量,适当提高铜镍的回收率,最直接有效的方式是降低精矿中滑石的含量。     

改性蛭石对有机污染物的吸附特性研究

用溴化十六烷基三甲铵对蛭石进行了改性,并研究了有机插层蛭石对水中萘胺、萘酚、苯胺、苯酚的吸附特性。结果表明:有机插层蛭石的层间距明显变大,对水中萘胺、萘酚的去除率可达90%以上,对苯胺、苯酚的去除率在80%左右。对有机污染物的吸附等温曲线符合Freund ish方程。有机插层蛭石对有机污染物的吸附既有水相与有机相之间的分配过程,又有物理吸附、静电吸附和离子交换吸附等吸附过程。     

银的赋存特征及其对选矿的影响

国内某大型银多金属矿,由于矿石性质的变化,导致银浮选指标和浸出率都发生了改变。为了查明影响银选矿指标的矿物学因素,使用光学显微镜、矿物自动分析仪(MLA)、扫描电子显微镜及X射线能谱分析等手段对矿石中银的赋存特征进行了系统的研究。结果表明,银主要赋存在辉银矿、银黝铜矿、深红银矿中,分别占64.19%、22.25%、10.37%,且银矿物与方铅矿等硫化物的共生关系紧密。银矿物主要以粒间银、包裹银的形式产出,分别占73.88%、22.27%,其中,包裹部分以脉石包裹为主,占13.47%。银矿物的粒度总体较细,集中在20~75μm,20μm以下部分占22.36%;尤其是20μm以下脉石包裹部分占6.81%,这部分银易损失到浮选尾矿中。矿石中方铅矿与闪锌矿的嵌布粒度较细,共生紧密,在磨矿过程中难以完全单体解离。根据上述研究成果,在保证银的选矿回收率、氰化浸出率,兼顾对铅、锌、硫进行综合回收情况下,建议首先通过银铅锌硫混合浮选后再分离的工艺获得银铅锌精矿和硫精矿,然后对银铅锌精矿进行再磨氰化浸出。