Recovery Of Gangue Research Articles

Closed-loop cleaning treatment system — resource recovery of coal gangue

ABSTRACT Coal gangue (CG) is one of the main solid wastes emitted by coal mining. It causes severe damage to the environment. CG contains high levels of valuable elements (Al, Si) and has the potential for utilization and clean disposal. Here, an environment-friendly process for separating valuable components from CG was proposed: the closed-loop system of activation-leach-separation. The results show that the decarbonization rate was close to 100% under the optimum conditions of CG particle size of 0.075 mm to 0.15 mm and activated at 800°C for 120 min. Subsequently, it was transformed into a mixed-acid system with a hydrochloric acid (HCl) concentration of 4.5 mol/L, hydrofluoric acid (HF) volume fraction of 15%, and the liquid-solid ratio of 10:1, which achieved excellent separation efficiency. The residual rate of Al in the solution was only 0.7%, and the extraction rate of Si can reach 71.6%. Further, industrial-grade AlF3 products were also recovered. By adding saturated KCl solution and reacting at 33°C for 15 min, Si was further recovered in K2SiF6, and the yield was 85.83%. Particularly, the leaching solution maintained good extraction efficiency in the subsequent three cycles, the yield of K2SiF6 was 88.29%, confirming the feasibility of the closed-loop system. This treatment embodied the environmental-friendly properties of low acid consumption and low effluent discharge, providing a feasible method for clean treatment and resource utilization of CG.

An exploratory study on strategic metal recovery of coal gangue and sustainable utilization potential of recovery residue

Coal gangue is a resource that is often improperly managed, especially during the current strategic metal element shortage. Achieving the efficient and green cooperative recovery of primary elements and strategic metal elements is critical, especially in the treatment without acid and alkali. In this study, the low-temperature combined roasting-DI water leaching method extracted valuable elements and prepared adsorption materials from coal gangue. The element migration and reaction mechanisms were investigated in detail. The results show that the primary reaction path includes the decomposition of ammonium sulfate into ammonium hydrogen sulfate, which reacts with kaolinite to form aluminum ammonium sulfate. Al, Fe, Ga, Li, Mg, Sr, Ti, and V were strongly correlated during roasting. The combined roasting of ammonium chloride and ammonium sulfate promoted the dissolution of Al and Li significantly. The specific surface area of water-leached gangue residue was adjusted by combined roasting, and its adsorption effect on lead ions was stronger than that of raw gangue and kaolinite. The present process presents an eco-friendly solution for the comprehensive utilisation of coal gangue.

Reducing entrainment of sericite in fine flaky graphite flotation using polyalurninum chloride

Polyaluminum chloride (PACl) was introduced as a flocculant to reduce the entrainment of sericite gangue in fine flaky graphite flotation. The dispersion and aggregation behaviours of sericite and fine flaky graphite in the absence and presence of PACl were studied by settling experiments and verified by optical microscope images. Results of batch flotation tests for artificial mixtures indicated that the addition of PACl decreased the recovery of sericite gangue and the water recovery. Zeta potential measurements, FTIR and XPS analyses revealed that PACl selectively aggregated sericite particles in terms of charge neutralization and precipitate enmeshment.

Improved flotation of PGM tailings with a high-shear hydrodynamic cavitation device

Fine liberated valuable particles are often lost to flotation tailings due to inefficient collection by air bubbles, and passivation of their surfaces by oxidation products and slimes when reclaimed from tailings dams. Extensive research covering a diverse range of technologies has been undertaken over the years to find feasible solutions to this problem, with only relatively minor success at an operations scale. A more recent and practical prospect which has already found application in the mining industry is the use of hydrodynamic cavitation devices (HCDs), causing the nucleation of ultrafine (nano) bubbles (NBs) on the surfaces of fine valuable particles, thus aiding their agglomeration and subsequent recovery by micro-bubbles (MBs) and normal sized (macro) flotation bubbles. This paper details investigations that have been undertaken on the Mach HCD reactor, using rougher, cleaner and recleaner feed samples sourced from a UG2 Platinum Group Metal (PGM) tailings operation. The results suggest that the formation of NBs and MMBs, together with enhanced cleaning of particle surfaces, were the dominant mechanisms. This not only lead to activation of valuable mineral surfaces but also depressed the recovery of gangue. The flotation kinetics were analysed using the modified Kelsall model, showing significant improvements in the maximum (fitted) recovery Rmax, together with a reduction in mass pull, for the optimum number of passes of the various feed samples through the reactor. The contributions to the increased recovery due to additional liberation of PGMs from the chromite grains and the increased gas holdup, are being investigated further.

Reverse flotation of cut-of-grade of Lakhra coal

ABSTRACTThe selective mining activities have generated a huge quantity of poor grade coal that is rich in mineral matter and sulfur content and has piled up in whole mining site at Lakhra. This highly oxidized and mineral matter rich coal has been upgraded by reverse floatation. Three process parameters such as pH (7, 8, 9, 10, 11), particle mesh size (60, 100, 150, 200), and % solids (10, 15, 20, 25, 30) in flotation pulp have been investigated with respect to their effect on sulfur and ash reduction. According to results of this study, parameters such as particle size of 100 mesh (150 µm), pH 9 and 20% solids were found to be optimum removing 63.7% of ash and 72.9% of sulfur from coal and coal recovery of 61.3%. Moreover, the heating value of coal also improved from 3924 kcal/kg to 5500 kcal/kg ~ 40.16% enhancement. The recovery of combustibles and gangue at optimum conditions was found to be 60.31% and 39.1% respectively. The clean coal thus obtained containing 12.7% ash, 1.5% sulfur, and 5500 kcal/kg heating value can be used as an energy source for cement manufacturing, in utility boilers, and production of smokeless briquettes for domestic and industrial use.

以黄土为中和剂的煤矸石及酸性矿坑水的综合处理实验研究

对煤矸石和酸性矿坑水的治理，无害化处理方法的研究已成为当前煤矿污染治理新的研究方向。本次研究一是矿坑水淋洗煤矸石脱盐的问题，二是以黄土为中和剂来解决煤矸石、矿坑废水混合液酸度过高来改善废水的水质问题。 The non-harmful treatment for the recovery of gangue and acidic pit water has been the new re-search field for the pollution management in coal mines. The present research consists of the desalinization by means of dripping pit water through gangue and the improvement of waste water by means of reducing the acidity of gangue and mixed pit water with loess as the neutralizer.

Anti-Depression Effect of Sulphuric Acid on the Flotation of Ilmenite

SYB2# (a category of hydroxamic acid) was employed as the collector of ilmenite flotation. Sodium carboxymethyl cellulose was employed as the depressor of gangue, and sulphuric acid as the pH adjustor of flotation. The effect of pH values on the recovery of ilmenite and gangue was investigated on the condition with (or without) depression respectively. The results demonstrate that pH value does not have any obvious effect on the recovery of ilmenite or gangue when no depressor is added. On the contrary, the pH value plays an important role in ilmenite flotation when depressor is added. To be specific, the recovery of ilmenite increases obviously with pH value decreasing. Having a comparison among the recoveries of ilmenite with different pH values adjusted by sulphuric acid, hydrochloric acid and nitrating acid, it is concluded that sulphuric acid produces anti-depression effect on ilmenite depressed by sodium carboxymethyl cellulose.

The effect of frother type and dosage on flotation performance in the presence of high depressant concentrations

The use of high dosages of polysaccharide depressants in order to depress the undesired naturally floatable gangue (NFG) present in ores beneficiated from the Bushveld Complex, South Africa, results in a significant decrease in the stability of flotation froths. These unstable froths can result in restricted mass pull and decreased valuable mineral recovery. Previous work using a single polyglycol ether type frother, DOW 200, has shown that an increase in frother dosage could be used to overcome the destabilisation of the froth to a certain extent and improve valuable mineral recovery. This resulted in an increase in water recovery and dilution of the concentrate by entrained material. This work extends this study to examine the effect of using a stronger frother, DOW 250, on the recovery of sulphide minerals and floatable gangue from a Merensky ore at different dosages of guar gum and CMC, which are typically used as depressants in the processing of Merensky ore. Results indicate that an increase in the strength of the frother resulted in a more robust froth. Depressant type also had an influence on results obtained.

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.

Surface tension of flotation solution and its influence on the selectivity of the separation between apatite and gangue minerals

This work presents and discusses the infl uence of the surface tension (γ LV ) of methanol/water mixtures on the fl otation response of apatite versus gangue minerals conditioned with fl otation reagents (75 g/t cornstarch and 100 g/t Berol 867) at pH 10.6. Berol 867 is a collector composed of sodium alkyl sarcosinate plus nonionic surfactant. The highest Schulz effi ciency of separation (recovery of apatite minus recovery of gangue) was achieved at ≈51.0 mN/m. The critical surface tension of wettability (γ C ) of apatite was found to occur at 34.7 mN/m when determined by means of gamma fl otation experiments, and it was 33.9 mN/m when determined by Zisman’s approach.

Balancing the reagent suite to optimise grade and recovery

The recovery of Platinum Group Metals and Gold (PGM + Au) from the UG-2 reef of the Bushveld Complex is an interesting challenge when the selection and optimisation of the reagent suite is considered. The UG-2 reef is characterised by two predominant gangue phases i.e. chromite and silicate, that have significantly different physical and chemical properties. A strategy needs to be devised to address concentrate grade that will reduce the recovery of gangue without significantly affecting the recovery of the valuable species. Recovery of the valuable species is complicated by the fact that PGM + Au occurs as a variety of different minerals having varying chemical and physical properties. The operating strategy has to consider the characteristics of the valuable mineral species and maximise recovery while meeting stringent grade specifications. Laboratory tests are conducted to illustrate the effect of the various flotation parameters. Applications of the findings on existing concentrators are discussed illustrating the need for a better understanding of the contribution of the various mechanisms occurring in the flotation cell. The paper demonstrates the significance of entrainment in the recovery of both valuable species and gangue species, and the need for a greater understanding of this non-selective sub-process on overall circuit performance. This paper forms part of a postgraduate study through the University of Cape Town into the development of a mechanistic model for the entrainment process. Although much work has been done in this study of the effect of various other parameters on the flotation of UG-2 ore, this paper focuses on the effect of frother, depressant and water on the flotation results.

The behaviour of wash water injected into a froth

Wash water is introduced into flotation froths to reduce the amount of entrained material reporting to the product. However, the behaviour of wash water in a froth is not well understood at present, and detailed information is sparse. The design of wash water delivery systems is currently based largely on trial and error. In the present study, experiments were conducted in a two-dimensional froth column to observe the movement of wash water in a froth, using various types of injector. Thus wash water was injected through a vertical pipe placed above the froth; through the same pipe immersed in the froth; and through a tee that resulted in two opposed horizontal jets. The movements of the wash water were observed, and quantitative liquid-fraction maps obtained, for each system. With the horizontal jets, vortex pairs were observed to form in the froth as a result of the wash water injection. In terms of their ability to spread wash water in the horizontal direction, the horizontal jets performed better than the vertical jet within the froth, which gave better results than the same jet falling on the free surface of the froth. The results show that whatever system is used, considerable back-mixing occurs between the froth and the added wash water, in the froth layer. Thus it is never possible to remove all the gangue particles from the flotation product. The best that can be done is to minimise the recovery of gangue by finding the optimum combination of the volume of froth beneath the injection point, the volume of froth above the injection point, and the gas and water flow rates. These observations are independent of the type of wash water distributor used.

99/03507 Mechanisms operating in flotation froths: Ross, V. E. Recent Adv. Coal Process., 1998, 2, (II), 109–144

The use of high dosages of polysaccharide depressants in order to depress the undesired naturally floatable gangue (NFG) present in ores beneficiated from the Bushveld Complex, South Africa, results in a significant decrease in the stability of flotation froths. These unstable froths can result in restricted mass pull and decreased valuable mineral recovery. Previous work using a single polyglycol ether type frother, DOW 200, has shown that an increase in frother dosage could be used to overcome the destabilisation of the froth to a certain extent and improve valuable mineral recovery. This resulted in an increase in water recovery and dilution of the concentrate by entrained material. This work extends this study to examine the effect of using a stronger frother, DOW 250, on the recovery of sulphide minerals and floatable gangue from a Merensky ore at different dosages of guar gum and CMC, which are typically used as depressants in the processing of Merensky ore. Results indicate that an increase in the strength of the frother resulted in a more robust froth. Depressant type also had an influence on results obtained.

Entrainment of Particles into Flotation Froths

Abstract Papers on entrainment in conventional froth flotation are reviewed and the results related to the structure of froths and their water content. The strong correlation observed between the recovery of gangue and the recovery of water, in both batch and continuous tests, is discussed and compared with the effect of water recovery on the recovery of hydrophobic (valuable) particles. Data on the structure and water content of flotation froths is summarized and an explanation sought for the way in which water, and hence entrained particles, are transported from pulp to froth column to concentrate.