Recovery Of Coarse Particles Research Articles

Evidence for surface cleaning of sulphide minerals by attritioning in stirred mills

Recent developments in large scale stirred milling technology using ceramic media have allowed its application to relatively coarse particle streams. Apart from benefits in grinding finer more efficiently, benefits may also be derived from the surface cleaning action of stirred mills. This paper discusses evidence for the cleaning action of a stirred mill on the surfaces of chalcocite and effects on its subsequent flotation. Single mineral samples of chalcocite were ground with either stainless or mild steel grinding media. The effects of surface contamination by iron hydroxide on chalcocite floatability were studied using ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) surface analysis and contact angle measurements. Depression of both coarse (+75 μm) and fine (−10 μm) size fractions was attributed to the surface precipitation of iron hydroxide species. Transfer of iron hydroxides from coarse particles to fine particles was observed with XPS analysis. Recovery of coarse particles (+75 μm) was improved by attritioning, while additional collector was needed to fully restore chalcocite recovery in both fine and coarse size fractions.

The formation of bubble clusters in flotation cells

We describe experiments in which the sizes of bubbles generated in a flotation cell were measured using high-speed video images. It was observed that in the presence of floatable solids, bubble clusters would form, held together by particles that attach to two or more bubbles and form stable bridges between them. The characteristics of clusters formed in the flotation of silica with dodecylamine (DDA) as collector, are reported. The size of the clusters is found to increase with increasing concentration of collector, probably because of its influence on the hydrophobicity of the silica. The mean size of bubbles within the clusters was generally higher than those that had not aggregated, suggesting that the rate of aggregation increases with increasing bubble diameter. The fraction of bubbles that were involved in clusters was found to increase with increasing DDA addition, reaching as high as 68 percent. There was a strong correlation between the fraction in clusters, and published values of the contact angle of DDA solutions and quartz. Previously unpublished photographs of bubble clusters rising out of industrial flotation cells are presented, that provide further evidence of cluster formation. The mechanics of cluster formation are discussed, and the implications for the modelling of the flotation process, and the performance of flotation cells, are explored. Clusters would be expected to lead to increased entrainment of non-floating particles into the froth in industrial cells, resulting in reduced product purity or grade. Cluster formation would be expected to increase the flotation recovery of coarse particles.

Role of Bubble Size in Flotation of Coarse and Fine Particles—A Review

Froth flotation is the dominating mineral beneficiation technique and has achieved great commercial success. This process has also found many applications in other industries where physical separation of materials is needed. However, its high process efficiency is often limited to a narrow particle size range of approximately 10–100 µm. Considerable efforts have been made to extend this size range to the lower limit of a few microns, even submicrons, and the upper limit of 1–2 mm, in response to increased needs for higher process efficiency and expanded applications of flotation. The particle–bubble collision, attachment, and detachment are the most critical steps in the flotation process. These individual elementary processes (microprocesses) and their effects on flotation efficiency are discussed and the most recent findings are reviewed. The low flotation recovery of fine particles is mainly due to the low probability of bubble–particle collision, while the main reason for poor flotation recovery of coarse particles is the high probability of detachment of particles from the bubble surface. Fundamental analysis indicated that use of smaller bubbles is the most effective approach to increase the probability of collision and reduce the probability of detachment.

Distribution of reagents down a flotation bank to improve the recovery of coarse particles

Collector and frother are commonly used to induce the floatability of valuable minerals in flotation plants. These reagents can be added in a conditioner prior to flotation or stage distributed along the flotation banks. A review of the literature and some experimental results obtained from laboratory and full-scale trials indicate that the way flotation reagents are distributed down a flotation bank can positively influence the flotation response of coarse particles. This paper summarizes these observations, which show that the distribution of reagents is a potential tuning variable for the optimization of the flotation process.

The flotation of pyrite using mixtures of dithiocarbamates and other thiol collectors

This paper presents results which show that when mixtures of dithiocarbamates are used to float pyrite each component has a synergistic effect on the performance of the others. In particular cyclo-hexyl dithiocarbamate which produced the lowest recovery when used as a pure collector had a significantly advantageous effect on recovery and grade when mixed in small quantities with another dithiocarbamate. Different molar ratios of cyclo-hexyl (oC6) and di-n-propyl (di-n-C3) dithiocarbamates (DTC) in the mixtures were tested. In all cases 90:10 and 10:90 mixtures produced higher recoveries and grades than did 50:50 mixtures or the pure components. Recoveries increased from 74.0% for pure oC6 DTC and 83.5% for pure di-n-C3 DTC to 89.5% for the 90:10 mixture. Grades increased from 14.5% for pure oC6 DTC and 18.5% for pure di-n-C3 DTC to 20.5% for the 50:50 mixture. The effect of mixtures was less marked at higher dosages indicating that for the same performance lower dosages of mixtures were required compared to those required by the pure components. The mixtures resulted in faster rates of flotation as well as a greater recovery of coarse particles. Increased recoveries and grades were obtained in the first minute due to an enhancement in the rate of flotation. When mixtures were used the p 50 of the concentrate increased showing that coarser material was collected. This effect was greater in the first concentrate than the final concentrate. Mixtures of dithiocarbamates and other thiol collectors, viz. xanthate, sodium mercaptobenzothiazole and dithiophosphate further enhanced recoveries and grades to a maximum recovery of 96.0% and grade of 21.0% for a mixture of 90% potassium n-butyl xanthate (PNBX) and 10% oC6 DTC. The method (premixing or separate) and sequence of collector addition had little effect on recoveries or grades. The effect of copper sulphate addition varied. In the case of cyclo-hexyl dithiocarbamate, the addition of copper sulphate dramatically reduced recoveries and grades but when other collectors were present this did not occur. Generally the addition of copper sulphate slightly enhanced recoveries and grades and greatly enhanced water recoveries probably due to a froth stabilization effect.

The effects of solids and reagents on the characteristics of coal flotation in columns

The effect of solids and chemical addition on column flotation of coal was investigated by examining the changes in the flow characterization and flotation performance. It was found that larger feed particles reduce the stability and the thickness of froth zone. While the addition of collectors (kerosene) increases the coal particle surface hydrophobicity, thus accelerating the froth collapse, bubble coalescence, and reducing the gas holdup; adding a frother increases the ratio of recovery of coarse particles (+200 μm) to that of fines. Using Dowfroth 250 as frother resulted in higher recovery and flotation rate constants, as well as the recovery of larger particles than in the case of MIBC. A method for predicting the bubble loading in flotation columns is proposed.

An evaluation of the role of particle size in the flotation of coal using different cell technologies

A large variety of new flotation cells has been introduced in the last few years, probably as a result of the successful introduction of column flotation in the minerals processing industry. In common with the column cell, a number of these new cells employ an essentially quiescent separation zone. However, a number of novel cell designs have been introduced that use agitation mechanisms similar to those employed on conventional flotation cells. The aim of this investigation was to evaluate flotation behaviour in both an agitated and non-agitated environment, particularly with respect to particle size. A hybrid ‘agitated’ column cell was designed for the investigation, and the operation of this unit was compared to that of a column cell, and to a batch flotation cell, on a laboratory scale. The testwork was conducted on coal fines, as problems with the flotation of coarse coal particles in a column cell had previously been identified. It was demonstrated that the addition of an agitated stage to a column cell can significantly improve the coarse particle recovery in comparison to the conventional column cell, while maintaining good selectivity in the fine sizes.

Flotation of coarse particles in a counter-current column cell

The effect of particle size on the flotation of coarse particles is analyzed. It is concluded that turbulence and the presence of the froth layer are detrimental to the recovery of coarse particles during conventional flotation. A counter-current column cell is proposed to avoid these two factors. In this column, a net upwards flow of water is prevalent, such that no froth is allowed to form on the top. Also, the levitation of heavy bubble-particle aggregates is helped by the ascending water current. Preliminary work at laboratory level with kilogram-size samples indicated that under similar conditions recoveries in the column were much higher than in conventional cells. Flotation results obtained with coarsely sized phosphate and quartz samples are presented. One interesting feature of this type of column is very fast flotation kinetics. Thus, a short column (only 55-cm collection zone) yielded full recovery of floatable values.

Deteriorative effects of both usage and long-term storage on aircraft and missile hydraulic fluids : R. F. Connelly and L. E. Gatzck, J. Eng. Ind., 83 (2) (1963) I51–155

Thiol collector mixtures are commonly used in the flotation of base metal sulphides and platinum-bearing ores. There are synergistic benefits claimed for these collector mixtures, with mixtures lowering total dosage requirements, improving coarse particle recovery and the rate of flotation.Some of these co-collectors are known to have frothing effects. Therefore, the aim of this study was to decouple froth and pulp effects and to consider only the bubble-particle attachments in the pulp. This was achieved through microflotation experiments, where various ratios of the ethyl and isobutyl chain lengths of xanthates, dithiocarbamates and dithiophosphates were used as collectors. The flotation recoveries and rate constants of galena were analysed as a function of particle size in order to determine whether collector mixtures produced any beneficial effects over those of using single collectors.Mixtures of ethyl xanthate with ethyl dithiocarbamate were shown to significantly increase rate and recovery of galena flotation above those of the single collectors. Mixtures of ethyl xanthate and ethyl dithiophosphate showed smaller improvements in recovery. However, isobutyl xanthate, as a single collector, was superior to the mixtures in all cases.