The role of the reagent suite in optimising pentlandite recoveries from the Merensky reef

The Platinum group elements (PGEs) in the Merensky Reef in the Bushveld Complex are strongly associated with the sulphide minerals, particularly pentlandite which contains significant amounts of PGEs such as palladium and rhodium in solid solution. The various operations use different reagent combinations in the flotation process to recover PGEs from the Merensky Reef which include primary and secondary collectors, copper sulphate (CuSO₄) as an activator and depressants, either carboxymethylcellulose (CMC) or modified guar gum (guar). This study examines the effect on two different ores, A and B, using dibutyl dithiophosphate (DTP) as a secondary collector in combination with sodium isobutyl xanthate (SIBX) as primary collector, the point of collector addition (mill or cell), the use of CuSO₄ addition, sequence of CuSO₄ addition and the effect of depressant type on the floatability of pentlandite, and shows that pentlandite floatability in contrast to that of chalcopyrite is reduced when reagents were added to the cell rather than the mill together with CMC. This effect was not observed with the use of guar gum as the depressant.     

Froth flotation of a Merensky Reef platinum bearing ore using mixtures of SIBX with a dithiophosphate and a dithiocarbamate

The Bushveld Igneous Complex (BIC) in northern South Africa has the largest deposit of platinum group elements (PGEs) in the world. In trace amounts, these are closely associated with base metal sulphides (BMS). Froth flotation is used as a bulk sulphide recovery to beneficiate these PGE ores. To maximise the recovery of the PGEs it is required to improve the recovery of the BMS. The chemical additives used largely determines the performance of the froth flotation process. Consequently, mixtures of collectors were used in batch froth flotation tests in an attempt to improve concentrate grades and recoveries of BMS from a Merensky Reef platinum ore. The mixtures consisted of a xanthate (SIBX) with a dithiophosphate (DTP) or a dithiocarbamate (DTC). Each mixture was tested at mole ratios of 80:20 and 60:40, with the xanthate the major component. An increase in nickel recovery was observed with all mixtures relative to pure SIBX at the expense of concentrate grade. The mixtures of DTC with SIBX increased the cumulative nickel recovery by 11%, while the mixtures with DTP increased it by 10%. Copper recovery increased by 6% with the DTP mixtures. No significant improvements in the copper recoveries and grades were observed with the mixtures of SIBX with DTC compared to pure SIBX.     

The effect of the reagent suite on froth stability in laboratory scale batch flotation tests

In batch flotation tests conducted on ores from the Merensky reef, changes in froth stability invariably occur with variations in the reagent suite. The main reagents are collectors (primary and secondary), activators, depressants and frothers. Since the particles entering and leaving the froth in a batch flotation system are continuously changing, the stability of the froth can vary. Under these conditions the simplest measure of froth stability is the measure of water recovery at a fixed froth height. The batch flotation system developed at UCT allows for the separation of gangue which is entrained relative to gangue which is floated. It has been found that the presence of naturally floatable gangue (NFG) leads to froth stabilisation, whereas the presence of hydrophobic sulfide minerals may lead to destabilisation of the froth depending on the hydrophobicity (contact angle) of the sulfide minerals. This can vary with ore type since particle shape and amount of particles present can influence the extent of destabilisation. At low depressant dosages sodium isobutyl xanthate (SIBX) always results in lower froth stability than sodium ethyl xanthate (SEX). The frothing nature of dithiophosphate leads to increased froth stability and the addition of copper sulfate results in destabilised froths. Increasing depressant dosage reduces the stabilising influence of NFG and the depressant type (guar gum or CMC) also affects froth stability. Frother can be used in an attempt to overcome the destabilising effects of high depressant dosage. This work examines the effect of variations in the reagent suite and uses water recovered at a fixed froth height as an indication of froth stability in order to analyse these effects on the recovery of sulfide minerals, floatable gangue and entrained gangue.     

The effect of molecular weight on the adsorption and efficacy of polysaccharide depressants

Long chain polysaccharide polymers, such as carboxymethyl cellulose (CMC) and guar gum, are commonly used in flotation to depress gangue minerals. These depressants are in widespread use in the flotation of platinum group minerals contained in the Merensky ore body where the dominant gangue minerals are talc, pyroxene and feldspar. The molecular weight and degree of substitution of these polysaccharides are known to be significant factors influencing the behaviour of such depressants. In the present study CMC and guar at different dosages and with different average molecular weights were used to investigate their effectiveness in depressing gangue minerals. The high molecular weight depressants ranged between 600,000 and 700,000 g/mol and the low molecular weights, 40,000-70,000 g/mol. The depressants were tested using microflotation, batch flotation and equilibrium adsorption studies. The investigation showed that, at starvation dosages (100 g/t) during batch flotation, the high molecular weight polymers did not depress naturally floating gangue (NFG), whereas the low molecular weight depressants did. At higher dosages (300 g/t), both high and low molecular weight polymers depressed all NFG, without depressing sulfide recovery in the pulp. The high molecular weight polymers were significant froth destabilisers, which suggested that they were acting as good slime cleaners. This, combined with their ineffective depression of NFG at low dosages, suggested that the high molecular weight polymers were selectively adsorbing to hydrophilic gangue (pyroxene and feldspar). Adsorption isotherm experiments gave the maximum adsorption densities attainable at equilibrium. These were compared to the adsorption densities of the polymers in the microflotation and batch flotation experiments. This information showed that very little polymer was required to destabilise bubble-particle interaction during microflotation tests. At conventional plant depressant dosages of 100-300 g/t, adsorption densities range from ∼20% to 50% of maximum.     

The response of sulphide and gangue minerals in selected Merensky ores to increased depressant dosages

Depressants are added to flotation circuits to reduce naturally floatable gangue (NFG) present in ores, but under certain conditions have been shown to affect sulphide mineral recovery, particularly guar reducing the recovery of pyrrhotite. Copper sulphate is added to increase sulphide mineral recovery, but may also activate gangue particularly in the presence of dithiophosphate. This has also been shown to vary with ore type. Previous work has shown the usefulness of analysing reagents holistically, decoupling pulp and froth effects and assessing material recovered by true flotation and that recovered by entrainment separately. This work assesses the effect of copper activation on different ores and the ability of two classes of depressants, guar gum (guar) and carboxymethylcellulose (CMC) to reduce this effect and shows that by a depressant dosage of 300 g/t almost all the NFG had been removed from the concentrate. It also evaluates the effect of depressants on the sulphide minerals and shows that pyrrhotite was most affected.     

重晶石浮选研究现状

本文在总结重晶石浮选回收工艺的基础上,介绍了重晶石浮选过程中所用捕收剂和抑制剂的研究和使用现状,并对重晶石浮选的发展方向进行了展望,指出开发新型高效浮选捕收剂和抑制剂,以及加强组合药剂的理论研究将是以后重晶石浮选的重点发展方向。     

硫砷矿物浮选分离药剂的研究进展

综述了毒砂浮选常规抑制剂和捕收剂的研究进展,特别介绍了近年来报道较多的毒砂组合抑制剂、组合捕收剂和新型药剂在含砷硫化矿石浮选分离中应用的研究成果,同时对含砷硫化矿浮选药剂今后的发展方向进行了展望。     

The effect of increased frother dosage on froth stability at high depressant dosages

High energy costs required to smelt low grade concentrates could be alleviated by the production of high grade concentrates. Obtaining maximum PGM recovery by the use of high dosages of polysaccharide depressants may be problematic in that a significant decrease in the stability of the froth, particularly with CMC, results. These highly unstable froths may result in restricted mass pulls and decreased valuable mineral recovery. There are a number of ways of counteracting unstable froths, such as increasing airflow rate, reducing froth height or increasing frother dosage. Although necessary to maximise PGM recovery, all of these are likely to lead to increased water recovery and dilution of the concentrate by entrained material. This work examines the effect of increasing frother dosage on the recovery of sulphide minerals and floatable gangue from a Merensky ore at varying dosages of guar gum and CMC, as well as on the recovery of entrained gangue and its dependence on the physical nature of the flotation pulp.     

Investigation on alternative depressants for iron ore flotation

Iron ore concentration through flotation represents an important application of reagents in mineral processing. Nowadays all Brazilian iron ore concentrators use starch as iron oxides depressant. This study evaluated the application of other depressants, which are commonly used in other flotation systems. Six carboxymethylcelluloses, three lignosulphonates, one guar gum, and four humic acids samples were investigated in the reverse cationic flotation. Laboratory flotation tests showed that only two polymers (one carboxymethylcellulose and guar gum) reached the same performance as starch. The superior performance of these reagents was due to the presence of the glucopyranose ring. The use of polymers blends led to promising results.     

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.     

氧化锌矿浮选药剂研究概况

从捕收剂、调整剂、起泡剂等方面总结了近年来国内外氧化锌矿浮选药剂的研究进展,强调了氧化锌浮选捕收剂的重要性.     

铌矿浮选药剂研究进展

评述了铌矿浮选药剂的研究进展及工业应用。分别阐述了胺类阳离子型捕收剂和羟肟酸、膦酸、胂酸、脂肪酸等阴离子型捕收剂与铌矿物的作用机理和应用现状, 从浮选性能、匹配的浮选流程、经济效益以及环境保护的角度评价了各类捕收剂的优缺点: 虽然胺类捕收剂工业应用广泛, 但存在浮选流程长、铌损失大、耗酸多的缺点; 羟肟酸类捕收剂选择性好, 但捕收能力较弱, 药剂用量大、成本高; 膦酸和胂酸类捕收剂捕收能力和选择性都较好, 但对环境危害大。概述了铌矿浮选调整剂的研究进展, 指出了脉石矿物有效抑制剂是铌矿浮选调整剂研究的重点。最后指出铌矿浮选药剂的发展方向是高选择性、低毒、低成本、绿色制备。     

The flotation behaviour of chromite with respect to the beneficiation of UG2 ore

The UG2 reef of the Bushveld Igneous Complex in South Africa is a valuable source of platinum group metals (PGMs) that is beneficiated by flotation. Chromite is one of the main gangue consituents of UG2 ore and it is essential that the amount of chromite reporting to the concentrate during flotation be minimised since it is detrimental to the subsequent smelting operations. It is generally considered that chromite is naturally hydrophilic and only reports to the concentrate by entrainment. However, it is possible that, under certain conditions, the chromite can be activated by the typical reagent suite used in the flotation of UG2 ore, rendering it hydrophobic and amenable to true flotation. The aim of this work was to investigate the effect of copper sulphate and the collectors, sodium isobutyl xanthate and dithiophosphate on the flotability of chromite in a microflotation cell. The effect of copper sulphate on the zeta potential of chromite was also determined. It was found that collectors alone have an insignificant effect on the flotation of chromite whereas, in the presence of copper sulphate recoveries of above 60% were observed in mildly acid to mildly alkaline solutions decreasing 20% at a pH value of 10. The extent of activation depended on the copper sulphate dosage. Zeta potential measurements showed that, above pH 4 copper species were adsorbed on the chromite and between pH 5 and 9 the adsorption lead to charge reversal of the chromite particles to positive values. The speciation programme, MINTEQA2, was used to predict the copper species present over the pH range used. It was postulated that the activation is due to the adsorption of copper hydroxide species at the chromite surface, which then act as sites for collector adsorption.     

钛铁矿浮选药剂及其作用机理研究进展

原生钛铁矿石占有率高、品位低、嵌布复杂是我国钛铁矿资源的基本特征,采用传统的磁选工艺,钛铁矿回收率较低。相对于磁选工艺,浮选工艺在细粒物料回收方面具有显著的优越性,是微细粒钛铁矿回收的有效工艺。为了促进钛铁矿浮选工艺技术的进步,系统总结了钛铁矿浮选药剂的研究进展,综述了钛铁矿浮选药剂及其作用机理方面的研究成果。对研究与生产实践中常用的脂肪酸类、膦酸类、胂酸类、羟肟酸类等钛铁矿浮选捕收剂进行了逐一介绍;新型组合捕收剂结合了多种常规捕收剂的优点,是捕收剂开发与应用的重要研究方向;调整剂主要包括钛铁矿的活化剂和脉石矿物的抑制剂,这些药剂在脉石矿物与钛铁矿可浮性相当时,对浮选分离起着决定性的作用。结合现代测试分析方法,分析、综述了浮选药剂在矿物表面的作用方式,为钛铁矿的浮选提供了理论基础,为选矿工作者提供了技术参考。     

Investigation of the interactive effects of the reagent suite in froth flotation of a Merensky ore

Interpretation of the behaviour of reagents in flotation is made complex by the existence of secondary effects, which can override the desired effects that enable effective separation, in addition to a predominant role of a flotation reagent, and the incomplete liberation of the mineral particles. Moreover, accumulation of dissolved ions due to the water recycle and reuse practice in processing circuits, which alters the chemical environment in the pulp and impacts the overall performance of the process, adds to this complexity. Therefore, it is often challenging to precisely assess individual contributions of the reagents to the overall performance, and hence the need for a holistic approach in evaluating the behaviour of reagents in flotation. Factorial design of experiments offers such an approach. This study used a factorial design approach in an effort to determine the interactive effects between chosen flotation reagents; collector, depressant, frother and water quality on the metallurgical performance of a Merensky ore. Increasing the ionic strength of the plant water increased recoveries, and the effect on decreasing concentrate grade was minimal, therefore the practice of water recycle and reuse should not impose any adverse impact during beneficiation of the PGM-bearing ore from the Merensky reef. It was also observed that higher recoveries were obtained with high ionic strength plant water than high frother dosage, indicating that the use of saline water in froth flotation of certain ores can replace the use of frothers, thus reducing costs. The factorial design approach can be useful in evaluating the simultaneous effects of such variables in the flotation process, thereby giving better understanding of their overall effect on the whole process.     

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents > copper > xanthate > copper + xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)₂ and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.     

云母矿物浮选研究进展

云母是一种性能独特的层状铝硅酸盐矿物,用途十分广泛。本文详细分析了云母矿物的晶体结构、表面性质及浮选药剂与云母的作用机理,综述了云母浮选捕收剂和抑制剂的研究现状,探讨了云母浮选传统工艺、新工艺和新装备的研究进展及实际应用。最后提出了云母浮选存在的问题并展望了未来的研究趋势。     

Effect of ultrasonic preconditioning of pulp on the flotation of sulphide ores

The variables affecting flotation during ultrasonic preconditioning, i.e. pulp concentration, particle size and density, temperature, pressure, as well as ultrasound frequency and amplitude, were studied. An ultrasonic process for the batch flotation of sulphide ores from the Merensky reef in South Africa was designed to improve flotation performance, by selectively altering the surface properties of the target mineral particles. After ultrasonic excitation, the floatability of the sulphides improved significantly, and the silicates were also depressed to some extent. Compared to mechanical conditioning, ultrasonic radiation can improve the flotation rate, value grades and recoveries and reduce the dosages of flotation reagents appreciably.     

CMC和古尔胶对滑石浮选的抑制作用研究

通过浮选试验、接触角测量、动电位测定和红外光谱研究了弱碱性条件下羧甲基纤维素钠(CMC)和古尔胶对滑石浮选的抑制性能及作用机理。结果表明,弱碱性条件下CMC和古尔胶是滑石浮选的有效抑制剂,低用量古尔胶能较好地抑制滑石,古尔胶的抑制作用强于CMC;在CMC和古尔胶作用下,滑石一级浮选速率常数减小,浮选速率降低,回收率下降。CMC和古尔胶吸附在滑石表面,使滑石表面润湿性增强、可浮性变差;CMC使滑石表面负电性增强,古尔胶使滑石表面负电性减弱。阴离子CMC主要通过—COO-和—OH吸附在滑石表面,中性古尔胶主要通过—OH吸附在滑石表面。     

Reagents used in the flotation of phosphate ores: a critical review

Phosphate rock needs processing to reduce the content of gangue minerals such as silicates, carbonates, and clays to meet the requirements of the phosphate industry. Froth flotation method has been an important part of the concentration process since the 1920s and today, more than half of the world’s marketable phosphate is produced by froth flotation. The literature on the processing of phosphate rocks by flotation is critically reviewed. Commonly used collectors, depressants, auxiliary reagents, and their mixtures in the flotation of the phosphate ores were tabulated. The advantages and disadvantages of the reagent type and structure (e.g., ionic and nonionic) on flotation were criticized. Based on the literature it was concluded that using surfactant mixtures has certain advantages over single surfactant as synergistic effect between surfactant mixtures were observed at different experiments such as surface tension, contact angle, adsorption, and flotation.