Predicting plant scale flash flotation performance – Validation of laboratory methodology and applications for use

A method has been developed in which laboratory batch flotation test results can be used in conjunction with mineralogical analysis to determine whether an ore is amenable to successful recovery via the flash flotation processing route. In the original development work, using a high grade refractory gold ore, a direct correlation was found with the particle properties of the plant flash flotation cell concentrate and a concentrate produced by a targeted laboratory batch flotation test. The respective concentrates were observed to have nearly identical distributions of the target elements (Au, S and Fe) by size as well as almost identical liberation characteristics of the key mineral (pyrite) for flotation. A second ore from the same mine, but of significantly lower grade and different grinding characteristics has now been tested to determine if the same correlations exist that were observed with the previous work and to provide further insight into the differences between laboratory and plant response in order to potentially refine the procedure further and enhance its usability as a predictive tool.Testing of the second ore confirmed the original findings that a targeted laboratory batch flotation test can produce a concentrate with a target mineral (pyrite) distribution by size and liberation that matches the concentrate produced by the industrial scale flash flotation cell whilst treating the same feed material. Further to this, grades of the intermediate size classes in the laboratory concentrates were found to be similar to those of the plant flash cleaner cells.From the correlations in performance observed with both ore types in the laboratory batch cell and plant flash flotation cell, methodologies are proposed that can be used to determine:

• •whether a new ore could be treated by flash flotation in a plant with an existing flash flotation circuit;
• •whether a plant operating without an existing flash flotation circuit could benefit from installing one; and
• •the amenability of an ore to the flash flotation process for greenfield flow sheet development.

A step wise approach is given for each to allow the method to be applied to and adapted for other ores and valuable mineral types. The advantage of following this methodology exists in that no specialised equipment or analysis methods are required to perform the test. Standard laboratory equipment has been used throughout the test-work and mineralogical analysis performed via commercially available MLA. The procedure is kept as basic as possible to allow for maximum usability on sites where only essential laboratory equipment exists.     

Evaluation of the applicability of ultrasonic velocity profiling in conditions related to wet low intensity magnetic separation

The internal material transport and selection processes of the wet low-intensity magnetic separators (LIMS) are poorly understood; this calls for improved measurement techniques. In this work an ultrasonic velocity profiling (UVP) technique for measuring how material flow velocity varies with penetration depth is presented. A measurement depth of just a couple of centimetres would greatly improve the understanding of the separation process in a LIMS.When applied to flows of mineral suspensions with high volumetric solids concentration, similar to those in the separators, UVP is unique in combining:

• •Non-intrusive measurements.
• •Operates using just one sensor element (transducer).
• •Relatively good spatial resolution.
• •Penetrates opaque suspensions.
• •Fast sampling rate.

Here, flows are studied in a rectangular duct (50 × 75 mm). Using magnetite suspensions, measurement through the whole depth of 50 mm is made with good accuracy. Velocity profiles are presented for solids concentrations of 5% and 9% solids by volume (20% and 36% by weight). Even at 9 vol% solids it is possible to reach a penetration depth of more than 25 mm.     

Variability and quality in ASR data represented by the Sandia model

• 1.1 The Sandia Model has been extended to yield individual parameter uncertainties and a measure of data quality.
• 2.2 Parameter uncertainties are small (1–3%) where there are a large number of degrees of freedom and the model is appropriate (Q < 1.0).
• 3.3 Data analysis suggests that the Sandia method, as published, calculates only the ‘residual stress’ in the sample but that the data might be used to determine in situ stress if core retrieval time is allowed for.

     

Is progress in energy-efficient comminution doomed?

Comminution is known to be an inefficient user of energy. This makes it the largest energy consumer in many mine sites and therefore a large component of cost. One would therefore have thought that improving comminution energy efficiency would be receiving the undivided attention of the mining industry, but this is not the case. This paper considers why this is so and what the future might hold, by posing and attempting to answer three questions:

• •Is this really an important issue for the mining industry?
• •If so, can comminution energy be substantially reduced in a reasonable time frame?
• •What are the drivers that will motivate change, and what should now be done?

The conclusions of the paper are pessimistic in the sense that forces may be gathering that will demand that the issue be addressed across the industry in the relatively near future, but optimistic in the sense that there is a clear development path. There is much that can be done with what is already known, and considerable promise exists in new developments which can be realised through sustained and focused R&D, building on new knowledge acquired in the last 20 years. These are outlined in the paper. It is concluded that there is a case for a global initiative to significantly reduce comminution consumption over say the next 10 years through a partnership between all parts of industry and the research community, covering short, medium and long-term innovation.     

The shear strength of reinforced rock joints

The evaluation of the shear strength of rock joints, reinforced by means of steel dowels, by both experimental measurements and numerical modelling with the aim of determining a provisional tool for optimization of dowel design is presented. The influence of some important parameters of both the rock and the steel type on the mechanical behaviour of the reinforced structure has been studied. The analysis of the mechanical behaviour of the discontinuous rock mass-dowel system presented in this paper involved the following theoretical and experimental studies:

• ••|laboratory tests on reinforced rock joints,
• ••|Finite Element Method (FEM) modelling of the laboratory tests,
• ••|analytical models for determination of the reinforced joint shear strength,
• ••|comparison between the experimental and analytical results.

The tests have been carried out in order to evaluate the influence of some important parameters on the mechanical behaviour of the reinforced structure:

• ••|steel type,
• ••|bar diameter,
• ••|reinforcement type (bars and tubes),
• ••|rock material type.

Shear resistance is heavily influenced by the quoted parameters. Yielding steel provides the highest contribution to the global reinforced joint shear resistance when using bars or tubes. Stronger and stiffer rock materials lead to higher shear stresses in the steel and consequently lower overall resistance.Two different mechanisms of reinforcement failure have been observed while varying the rock material characteristics. The analytical model has been set up in order to reproduce these two failure mechanisms, one involving a strong and stiff rock material with bar failure determined by shear and tensile stresses at the joint intersection; and the other involving weaker rock and the formation of two symmetric plastic hinges in the bar, with failure being due to either the tensile strength or the ultimate elongation of the reinforcement being reached. Finally, the analytical model has been validated by comparison with experimental results.     

Separation of feldspar from quartz using EDTA as modifier

A study was conducted to test a new technique for separating quartz from feldspar using EDTA as modifier in acid medium.The aim is to replace the modifier now in use, namely HF, because of the growing awareness of environmental and health problems.The research was carried out using a multiple approach including: zeta potential measurements and flotation tests with the EMDEE Microflot system.Comparison and correlation of the results of these experiments leads to the following conclusions:

• &#x02022;- It is possible to separate quartz from feldspar at around pH 2 using EDTA as modifier.
• &#x02022;- Of the tested collectors (cationic and cationic-anionic) the best results are obtained with a mixture having a ratio of 3 cationic to 1 anionic.

     

A review of methods to model the froth phase in non-steady state flotation systems

The current of batch flotation froth modelling is critically reviewed in order to identify its significance and usefulness, particularly in the scale-up of batch data to a continuous flotation process. This review suggests that the concept of the froth recovery factor, R_f, may provide the most useful way of establishing the performance of the froth phase in a batch flotation process. The froth recovery factor refers to the fraction of material reporting to the pulp-froth interface which is ultimately recovered in the concentrate. It is also proposed that a froth recovery model based on froth retention time can be used for relating batch froth performance to continuous flotation systems. However, a quantitative model which relates the froth recovery factor and froth sub-processes has yet to be developed.     

Die Erneuerung der Klinkerproduktion der Zementwerk LEUBE GmbH in St. Leonhard/Österreich

After conducting intensive studies as well as a feasibility study, Zementwerk LEUBE GmbH has taken the decision to install a new kiln line. Aims of the project were high fuel substitution rates, low energy consumption as well as lowest possible emissions simultaneously with a high degree of flexibility of the plant. The project investment of approximately 31.5 mio. € includes as follows:

• Raw meal dosing
• 5-stage preheater with calciner and combustion chamber in concrete structure with steel platforms
• Shift of an existing rotary kiln
• Kiln hood and grate cooler
• Cooler exhaust air filter
• Fuel handling (alternative fuel for calciner)
• Clinker transport
• Necessary connections to existing feeding and exhaust gas handling

The project was executed by a LEUBE team with a specialized EPCM-team (Engineering Procurement Consulting Management-Team) from A TEC Production & Services GmbH. The project started on 22 July 2009. The first clinker was produced on 20 October 2010 after an accident-free total erection phase of 15 months. After more than 4 years of production experience it can be summarized that all expectations and all guarantee values have been completely fulfilled. The yearly reduction of coal consumption amounts to approximately 8000 tons which correspond to a fuel substitution rate of approximately 70?%. The electric power consumption was reduced by approximately 20?% compared to the old kiln lines. The strict emission limits in the tourism area of Salzburg could be met without any difficulties. With the new kiln line it is possible to adapt the production according to the seasonal fluctuating cement sales (the production ratio is between 1000 tpd and 2000 tpd clinker). The system demonstrates an extremely high degree of flexibility in terms of different fuels, raw materials and throughput. Additional modifications in the area of raw mill and exhaust gas filter were effected in 2011/2012, which secures the clinker production at the plant in St. Leonhard in the future.     

Potential use of carbon felt in gold hydrometallurgy

The use of carbon felt as a three-dimensional electrode appears to be very promising for the recovery of heavy metals, and toxic compounds removal from dilute solutions, considering its favourable physico-chemical properties: high specific surface area, good fluid permeability and compressibility, chemical inertness and good electrical conductivity.This work presents the contribution of the carbon felt electrode in two different steps of the gold cyanidation recovery process

• &#x02022;- firstly as a cathode for the electrowinning of gold solution obtained after the elution of loaded carbon;
• &#x02022;- secondly as an anode for the electro-oxidation of cyanide ions present at low concentration (200–300mg/l) in waste streams.

In the first case, more than 10 kg of gold per m² of felt (2000 kg of gold per m³ of felt) can be loaded at 400 A/m² from dilute gold solutions (30 mg/l Au) with classic Faradic yields (6–12 %) and high overall extraction efficiency (>90 %). The felt homogeneously loaded with adhesive gold deposit can be smelted in an electric furnace without addition of fluxes since the carbon felt decomposes in gaseous products without formation of ashes.In the second case, the cyanide ion concentration can be lowered to as low as 10 mg/l by electro-oxidation to cyanate form (CNO⁻) at 400 A/m² in the anodic compartment of a divided cell. The presence of copper ion significantly improves the current efficiency of this electro-oxidation and sharply reduces the oxidation of the carbon felt. Copper ions accelerate the oxidation rate of free cyanide ions through the formation of easily oxidizable complexes owing to a mechanism in which the Cull Cu^ll redox couple acts as an electron transfer mediator.     

Relationship between the bubble surface flux that overflows and the mass flow rate of solids in the concentrate of flotation processes

This paper presents the relationship between the bubble surface flux that overflows and the mass flow rate of solids in the concentrate. Even though this study was carried out in a flotation column, the knowledge derived from this paper may be applied to all froth flotation processes. The experimental set up was equipped with an image analysis system to estimate the froth bubble diameter and the air recovery. This study describes the difference between the bubble surface flux entering the froth zone (S_bI) and the flux that arrives to the top of the froth (S_bT) and then overflows to the concentrate (S_bO), the latter being most directly related to the mass flow rate of solids in the concentrate. It was observed that the superficial area of the overflow increased with increasing collector addition and air flow rate, but decreased with increasing froth depth and particle size distribution. Visual evidence and experimental results suggest that, it is common that the superficial area of air that overflows in the concentrate is covered by particles. Only when this condition is almost achieved does overflows occur; otherwise, a high level of coalescence and bubble bursting take place at the froth surface. This was concluded after finding compatible trends between the estimated and predicted mass flow rates of solids in the concentrate, when a tractable geometrical model was used (R² = 0.8).     

Effect of entrainment in bubble load measurement on froth recovery estimation at industrial scale

Froth recovery was calculated in a 130 m³ mechanical cell of a rougher flotation circuit. This was done by bubble load determinations along with mass balance surveys. Valuable grade in the bubble load decreased in the −38 μm due to fine particles entrained to the chamber of the device. The effect of fine particle entrainment on froth recovery was evaluated. A comparison between results from the raw bubble load data (assuming all particles were transported by true flotation) with those from corrected bubble load information (subtracting fine particle entrainment) was carried out. Entrainment occurred due to hydraulic transport in the bubble rear, which corresponds to the worst case scenario for froth recovery estimation. Results showed that the relative error was less than 0.3%, which allowed validation of the bubble load measurement as an effective methodology for froth recovery estimation at industrial scale.     

Effects of frother type and froth height on the flotation behaviour of chromite in UG2 ore

About 70% of the UG2 reef consists of the gangue mineral chromite (FeO · Cr₂O₃). In the processing of UG2 ore by flotation for the recovery of platinum group elements (PGEs) the presence of chromite in the concentrates can cause serious downstream processing problems and a grade of less than 3% Cr₂O₃ is sought. This constrains operating procedures and compromises optimum recovery of the PGEs.In this study, the influence of the froth phase on the recovery of chromite was investigated by changing both frother type and dosage and froth height in batch scale flotation tests. The results obtained showed that it was possible to obtain concentrates with less than 3% Cr₂O₃ content by increasing the froth height, allowing for better drainage of both entrained gangue particles and coarse particles with low hydrophobicity. At a 3 cm froth height, very low water and mass recovery were obtained and thus low entrainment. Nevertheless a small amount of chromite particles coarser than 45 μm was persistently recovered which may be attributed to the true flotation of these particles.The mechanism of chromite recovery was discussed on the basis of the difference in the appearance of the froth structure and water recovery.     

The froth stability column: Measuring froth stability at an industrial scale

Froth structure and stability are known to play important roles in determining mineral flotation recovery and selectivity. However, measuring froth stability in a consistent manner remains a significant challenge, especially at an industrial scale. Following preliminary tests on a copper concentration plant, a quantitative dynamic stability measure is investigated in this study in order to extend the results over a wider range of conditions and on a different ore body. The technique is based on the Bikerman foam test and uses a non-overflowing froth column to quantify froth stability.Experiments were carried out using an automated version of the froth stability column under different operating conditions. Air flowrate was the key operating variable. Tests were reproduced on a single flotation cell of a Platinum Group Metals concentrator. The froth stability factor, β, was measured for each operating condition, and compared with the air recovery in the cell, α, which was measured using image analysis. The froth stability column results gave the same trends as image analysis. In particular the froth stability factor was found to be linearly related to the actual fraction of air overflowing the cell.The metallurgical results clearly indicated that changes in air flowrate result in variations in flotation performance that can be attributed to changes in froth stability. The results showed that high froth stability conditions occur at intermediate air flowrates, and result in improved flotation performance. It is found that the froth stability column is a simple, cost-effective and reliable method for quantifying froth stability, and for indicating changes in flotation performance.     

Impulse energy inputs to modify subsurface structure and functions and process properties of calcium-bearing minerals

Using Hammett indicators, X-ray fluorescence spectroscopy and atomic force microscopy, the authors analyze influence of high-voltage nanosecond impulses on structure and chemistry of surface and on process properties of calcium-bearing minerals. As a result of impulse energy inputs for t ≤ 30 s, the change in the structure and functions of mineral surface includes: enhancement of electron–donor capacity and formation of structural defects on the surface of fluorite, and enhancement of acceptor capacity of the surface of calcite and scheelite. Pre-treatment of mono-mineral samples by electrical impulses increases flotation ability of calcium-bearing minerals: increment in froth recovery makes 10–12% for scheelite, 5–6% for fluorite and 7–8% for calcite.     

Environmental pollution from coal mining activities in the Enugu area Anambka state Nigeria

Hydrogeological studies of the Enugu coal mining area were carried out which included hydrogeochemical analyses of water samples. These analyses revealed high sulphate and iron content in the acid mine drainage water as well as high total dissolved solids’ (TDS) and low pH (acidity) values. The water issues from the Ajali Sandstone formation and the underlying carbonaceous Mamu Formation and is classified as hard water. As a consequence of under-mining this aquifer, huge volumes of (polluted) water has flooded the mines are channelled into some streams or rivers which in turn get chemically polluted. Remedial measures have been indicated which include the following:

1. the treatment of acid mine water before pumping into streams or river;
2. the disposal of mine spoil wastes in carefully prepared and designed disposal sites;
3. planned and detailed mapping of the fractures in the Manu Formation for more effective dewatering scheme and increased exploitation of the overlying Ajali Sandstone aquifer to reduce or limit the amount of water flooding the mines in the underlying Mamu Formation.