Floatable Minerals Research Articles

Kinetic Response of Industrial Flotation Banks: Effect of Particle Size and Mineralogy

One of the main problems in current flotation plants and new projects is the significant decrease in feed grades and changes in the mineral composition, which has an important effect on the mineral liberation and associations. Additionally, flotation plants usually operate with a feed throughput higher than the original design, which has a significant impact on the feed particle size. All these conditions affect the metallurgical performance, and they must be evaluated and addressed by improving the control strategies for the optimization of banks. For this purpose, the flotation of valuable minerals along the circuits requires better understanding, considering the compromise between performance and selectivity in flotation circuits. This paper presents a characterization of the different minerals recovered along industrial flotation circuits. Plant sampling campaigns, performed in a copper industrial concentrator in Chile, provided the data for the study. Two rougher flotation banks consisting of cells of 130 m3 and 300 m3, were evaluated. All the samples from the industrial surveys were analysed by screening and mineralogy, and the mineral recovery along the circuits was evaluated per particle size class, liberation class, type of associations, and others. Additionally, operating data on froth depth profiles complemented the evaluation of the mineral composition of concentrate streams along the circuit. The results allowed for identifying and quantifying the main factors that affect the copper recovery and concentrate grade along the flotation banks. We found that minerals with liberation lower than 50% have a significant impact on the recovery. On the other hand, the decrease in the Cu grade in concentrates along the flotation circuits is mainly due to the relative increase of middling minerals (less liberated), non-valuable floatable minerals, such as free pyrite, and gangue entrainment. The characterization of the gangue entrainment flowrate along the flotation banks showed a strong relationship with froth depth, which becomes more critical towards the last cells of the banks.

The flotation behaviour of liberated Platinum Group minerals in Platreef ore under reduced reagent conditions

In spite of numerous studies on PGM behaviour in flotation, there remains much discrepancy regarding PGM speciation and its impact on floatability, as PGMs are routinely considered as an entire group for recovery prediction and trouble-shooting investigations. The understanding of preferential floatability of PGM species under a given flotation regime is important in predicting and addressing mineralogical variability in processing plants, to ensure efficiency in PGM upgrading and recovery. In this contribution, the effect of reduced collector and frother dosages on floatability of individual liberated PGM species was studied in Platreef ore from South Africa, which contains a large variety of different types of PGM species.Reagent tests were performed, with the aim to facilitate a more competitive environment for PGM flotation, by decreasing the collector and frother dosages with respect to a baseline test. Automated mineralogical analysis was performed on the feed, rougher concentrates and tails of the reduced reagent and baseline tests to ascertain how PGM species respond to reducing collector and frother dosages by virtue of the concentrate streams and tails they report to. PtS showed preferential upgrading compared to PdBiTe, PtPdS, PtBiTe, and PtAs, in the reduced reagent test. PdBiTe overall performs better than PtBiTe. PtAs consistently performs the worst in both baseline and reduced reagent tests and is therefore deemed a poorly floatable mineral irrespective of the reagent conditions used. PtPdS, PtAs and PtS floatability seem to be sensitive to grain size with coarse PGM preferentially recovered, over finer grains, in first concentrates.These results can aid in predictive studies for flotation of Platreef ores with variable PGM assemblages, and consequent tailoring of reagent conditions to improve flotation efficiency.

Flotation bank profiling revisited

Down-the-bank grade-recovery data are examined to determine whether the best performance could be correlated with balanced cell-by-cell recovery or balanced cell mass pull. Previous work had shown evidence in support of the former but here we show correlation with balanced mass pull may often be found. Balanced recovery seeks to maximize selectivity against a second floatable mineral while balanced mass pull seeks to maximize selectivity against entrained gangue. The choice, then, would appear to depend on the amount of second floatable mineral relative to entrainable gangue, but the case is made that choosing either balanced recovery or balanced mass pull is better than no choice. Most of the plants examined had forced air mechanical cells and used air rate to manipulate the bank. It is shown that using air further improves performance by controlling water recovery, and hence entrainment. Some observations on banks with self-aerated cells are included.

The practice of geological mapping of the Zhdanov deposit ores in the Kola peninsula

Geological mapping is included in each stage of geological prospecting. How detailed and consistent the obtained data are directly depends on how thoroughly an object has been studied. The main purpose of geological mapping is to identify areas with uniform ore and to give recovery projections. Gipronikel Institute has been engaged in such work for 30 years and has accumulated a great number of successful practices. As an example, this paper describes the results of geological mapping that was done for the Zhdanov deposit of copper-nickel sulphide ores in the Kola Peninsula. This study resulted in identifying geological types of ores (such as raw, refractory and talcose ores), which can be processed following the same process sequence but with different performance. The key differentiation criteria included the concentration of valuable components, the share of coarsely disseminated sulphides in the total amount of sulphides contained in a sample, the concentration of the easily floatable mineral — i.e. talc. Due to high variability in the material composition of striking and dipping ore bodies, the deposit has seen geological mapping conducted continuously for more than 10 years. Over that period, a database was created showing the distribution of different geological types of ore and the variability in the estimated recovery of nickel and copper, which is used for concentrator plant operations planning based on prospecting data.

Analysis of Industrial Flotation Circuits Using Top-of-froth and Concentrate Mineralogy

ABSTRACT The aim of this work was to study the true flotation process and entrainment contamination along flotation banks. For this purpose, a new approach for characterizing the recovery and grade profiles down the industrial flotation banks was developed and tested in two industrial rougher banks, of nine 130 m3 and six 250 m3 cells. The procedure consisted of feed, top-of-froth (TOF) and concentrate grades measurement together with mineralogical analysis down the bank. These data are useful for the assessment of liberation and association of floatable particles recovered into the concentrate (true flotation) and gangue entrainment. Results allowed for the quantification of the decrease of Cu grade in concentrates and TOF samples along the banks, due to the relative increase of middling minerals and gangue entrainment. The liberation coefficient of Cu sulfides significantly decreased down the banks, because of preferential flotation of middling particles after exhaustion of the free Cu sulfide minerals. The main difference between concentrate and TOF samples was the entrainment content, while the composition of floatable minerals was similar. Therefore, the TOF measurement and mineralogical analysis provides a simpler way to assess the flotation process down the industrial flotation banks. This knowledge is relevant for process diagnosis and for selecting control strategies for flotation banks operation and optimization (e.g., froth depth and gas flowrates profiles).

Quantifying mineral liberation by particle grade and surface exposure using X-ray microCT

Liberation is a key driver in all mineral separation processes as it limits the maximum possible grade for a given recovery. In flotation, this is further complicated by the fact that it is surface exposure of the floatable minerals that determines the ultimate performance. Liberation, grade and surface exposure are commonly quantified using Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis of polished sections. The intrinsically 2D nature of this technique can result in significant sampling errors and stereological effects that can affect the quantification of the ore’s textural characteristics. X-ray microCT (XMT) is an imaging method that can non-invasively and non-destructively delineate ore fragments in 3D, thus providing an alternative method that eliminates the need for stereological corrections and readily provides surface exposure. A methodology and automated algorithm were developed for extracting this information from images of closely packed particles. By dividing these particles into classes based on both their surface exposure and grade, the extent to which there is preferential breakage of the particles can be assessed—an important consideration if sufficient surface liberation for good flotation performance is to be achieved at coarser particle sizes. Using low energy scanning simple 3D mineral maps can be obtained via XMT, allowing for the assessment of liberation and surface exposure for each mineral species. The methodology was tested on low grade porphyry copper ore as this is representative of the most commonly treated ore types for copper production.

Investigation of effective operating parameters on carrying capacity in column flotation of copper sulfide minerals

ABSTRACTThe carrying capacity (Ca) in column flotation can be determined by experiments in terms of mass of solids per unit time per unit column cross-sectional area. The estimation of Ca has been typically defined by a simplified statement on the basis of representative particle size and the floatable mineral density. Although this statement encountered with several assumptions and limited ranges of the data that increase errors for other applications, in Ca expressions, the effect of particular variables, such as particle size, feed solids rate, bubble diameter, air flow rate, feed solid content, frother dosage, and froth height should be considered. In this study, the effects of these parameters on the Ca were investigated in column flotation using copper sulfide ore. It was found that when the feed solid rate increased, the concentrate solid rate increased to a certain point, whereafter it started to decrease. When the air flow rate increased, the Ca first increased then drastically decreased. In low feed flow rates, the increase in frother rate led to the higher carrying capacity, whereas in feed flow rates over 1.2 cm/s, the carrying capacity in frother rate of 45 ppm was more than 75 ppm. By decreasing the froth height and increasing the solid percentage (up to 30%), Ca increased. The results of the experiments at various feed particles sizes showed that the particles with size 45–63 µm had the maximum carrying capacity.

Bank profiling and separation efficiency

Various authors have discussed methods of optimising a bank of flotation cells. In this paper, JKSimFloat is used to investigate the effect of recovery profiling and mass pull profiling (i.e., mass distribution to cells in a bank) on the separation efficiency between floatable minerals and against entrained gangue.In the case of two floatable minerals, a balanced recovery profile was found to be optimal: supporting and extending previous analysis. In the case of separation of a floatable mineral from entrained gangue, the entrainment model that links water overflow rate to solids overflow rate was employed. When the value of b in the entrainment model is greater than one, a balanced mass pull profile was found to be optimum. The evidence for b>1 is briefly reviewed; no example has been found where b<1. Most of the profiles were controlled in the software by altering the bubble surface area flux distribution; a sensitivity analysis was performed using other variables.Recovery profiling was tested as part of a bank optimisation campaign at a talc operation in Timmins, Canada. Using air and frother as manipulated variables, it was found that as the rougher bank was moved toward a balanced profile the final plant product showed improvement in grade and yield.

An Overview of Optimizing Strategies for Flotation Banks

A flotation bank is a serial arrangement of cells. How to optimally operate a bank remains a challenge. This article reviews three reported strategies: air profiling, mass-pull (froth velocity) profiling and Peak Air Recovery (PAR) profiling. These are all ways of manipulating the recovery profile down a bank, which may be the property being exploited. Mathematical analysis has shown that a flat cell-by-cell recovery profile maximizes the separation of two floatable minerals for a given target bank recovery when the relative floatability is constant down the bank. Available bank survey data are analyzed with respect to recovery profiling. Possible variations on recovery profile to minimize entrainment are discussed.

Optimizing flotation bank performance by recovery profiling

This paper uses the first-order fully mixed model to argue that operating a bank of cells with a flat cell-by-cell recovery profile yields maximum separation between two floatable minerals with constant relative floatability for a target bank cumulative recovery. The bank optimization problem thus translates into a local problem of selecting cell manipulated variables, such as air rate, to reach that recovery profile. Some properties of the bank that emerge from the analysis are discussed. Recovery profiling appears to contribute to the success of air profiling recently reported.

Flotation rate distribution in the collection zone of industrial cells

The batch flotation process has been commonly characterized assuming a flotation rate distribution function F( k), e.g.: Dirac delta, Rectangular, Gamma or Weibull functions. The identification of F( k) for the collection zone of continuous industrial cells is more complex and to the authors knowledge, has not been reported yet. In this work, a novel procedure to estimate the flotation rate distribution from the collection zone of industrial flotation cells, using the radioactive tracer technique, is presented. The approach consists of measuring the impulse response of the floatable mineral tracer concentration, and non-floatable gangue tracer concentration (Residence Time Distribution, RTD), in the cell tailings. Then, the floatable tracer concentration can be compared with the model prediction, using the Gamma function and the RTD of the non-floatable tracer. Thus, the F( k) distribution parameters were obtained by means of the least-square estimation. The new approach was successfully tested in industrial rougher flotation cells of large size.

Froth recovery of industrial flotation cells

The mass flowrate of particles (ton/h), entering the froth by true flotation, was evaluated from direct measurement of bubble load (ton/m 3) and gas flowrate (m 3/h). This information, together with the concentrate mass flowrate, allowed the estimation of the froth recovery of floatable mineral in a 130 m 3 rougher flotation cell. It was found that mineral transport along the froth was mainly non-selective, and also the contribution of valuable minerals recovered by entrainment was negligible, if compared with minerals recovered by true flotation. Thus, a direct estimation of the froth recovery was obtained, without arbitrary assumptions about the grade of mineral transport by entrainment and drainage. This simple procedure allows a non-biased and independent evaluation of the effect that design and operating variables have upon the collection and froth zones performance, in large flotation cells. The use of this approach for flotation cells diagnosis and development of new control strategies is considered.

Influence of shape characteristics of talc mineral on the column flotation behavior

Column flotation, which is a very effective process in mineral processing especially for easily floatable minerals, is one of the most important new developments to emerge in mineral processing technology in the last years. In this study, the flotation behavior of talc products having different particle shapes produced by different grinding mills (ball and rod mill) was determined by using column flotation process. Shape characteristics of the particles were investigated by the two dimensional measuring technique based on the particle projections obtained from the SEM microphotographs using a COREL Draw 10.0 program. The results showed that particles possessing higher elongation and flatness properties were recovered better during column flotation, whilst roundness and relative width had a negative effect on the flotation behavior of the talc mineral studied. Consequently, as the shape of the particles produced by the mill deviated from the ideal sphere, their floatability was increased.

Effect of collection zone height and operating variables on recovery of overload flotation columns

This paper presents results of column flotation of silica sand ( d 80=190 μm ) that show typical column heights may adversely affect the performance of the flotation, when relatively dense flotation slurries of floatable mineral are processed. For slurry densities above 20% of solids (w/w), floated under typical conditions ( J g =1.46 cm/ s , J t =1 cm/ s , J ww =0.16 cm/ s , h f =0.3 m ), the bubble–particle aggregate reaches density values close to one losing their buoyancy. Under these conditions, mineralized bubbles accumulate, coalesce (losing a fraction of the particles that transport) and may even be carried out to the tailings discharge, affecting both the recovery and the processing capacity of the column. By reducing the height of the collection zone of the column ( h c) this abnormal operation may be substantially mitigated. In this work, recovery increased from 55% to 78% by decreasing h c from 4 to 1.5 m when processing a pulp with 30% of floatable minerals. The paper also discusses the effect of column height upon other important variables.

Determination of the contributions of true flotation and entrainment in batch flotation tests

Laboratory batch flotation tests were carried out on a deslimed (+6 μm) sulfiderich cassiterite ore, an ultrafine fraction (−6 μm) of a cassiterite ore and a bituminous coal. Chemical conditions were kept constant but the water recovery was varied by changing the height of the froth column and the rate and depth of froth removed. The recovery of the floatable mineral in each system was then found to be linearly related to the weight of water recovered. The intercept of the regression line on the mineral recovery axis, where the water recovery is zero, was interpreted as the recovery due to true flotation. The entrainment contribution was proportional to the slope of the line. In this way the contributions of entrainment and true flotation to overall recovery were separated.