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By D. F. Caicedo, I. A. Brum, L. A. Betancourt

Ferricyanide ()()*is one of the most stable cyanometallic complexes present in the gold mining effluents. This cyanocomplex is hard to degrade by natural attenuation and generates a negative impact on aquatic environments. Although free cyanide (CN-) can be obtained by acidifying the solution, the CN- is lethal for all forms of life. The oxidation of ()()* in a typical photocatalitic system was evaluated with the addition of H2O2. To verify the degradation, chemical parameters, such as free cyanide, the formation of ammonia, nitrate, and total iron were analysed at the end of the process. The degradations obtained were up to 70% in a heterogeneous photocatalysis system with TiO2, and a low rate of dissociation was observed by photolysis. The best result was achieved with the H2O2 and TiO2 photocatalytic system, and the stoichiometric concentration was about 2.5 times less than the peroxide used in the real gold mining industry, reaching 83% degradation. The photocatalytic process obtained less toxic byproducts than the original synthetic ferricyanide used as mining wastewater. Keywords: Cyanide, heterogeneous photocatalysis, titanium dioxide, UV radiation, gold wastewater

Jan 1, 2020

On behalf of the Council and staff of The South African Institute of Mining and Metallurgy, it is my privilege to wish all members and subscribers a very Happy Christmas and a Prosperous New Year.

Jan 1, 1988

By T. Mützea, L. Schützenmeister, G. Kacheb

High-Pressure Grinding Rolls (HPGR) are employed in cement plants worldwide. Although the technology has been mastered in the majority of applications, design-, scale-up- and operationalchallenges still exist today. In addition to modelling throughput, energy requirement and comminution success, the prediction and avoidance of malfunctions is of great importance in current research. The performance of the mill is highly influenced by the roll speed and the fineness of the feed material. Another parameter influencing the composition of mill feed is the circulating load, which is determined by the grinding circuit configuration, the target fineness and the separation efficiency of the classifier. In order to meet this circumstance and simultaneously maintain a reasonable level of material input and testing effort, a complete grinding circuit on a small technical scale was set up in the research centre of Thyssenkrupp Industrial Solutions AG. The present study varied the roll speed (0.5-2 m/s) and the proportion of fines in the feed (0-75 %) in order to investigate the influence of both parameters on the finish grinding of a Portland cement with a target fineness of 4000 cm²/g according to Blain. The experimental results are compared with model concepts and critically examined with regard to their transferability to industrial plants. Keywords: Cement grinding, grinding circuit, HPGR

Jan 1, 2020

By G. Mucsi, F. Kristály, R. Szabó

Kaolin is one of the most important ingredients in porcelain manufacturing. Its main phase is clay mineral containing aluminum hydrosilicate, namely kaolinite. Beside kaolinite it also contains quartz, illite and feldspars, which impair its applicability. Kaolin is a non-reactive material, but metakaolin can be produced by heat treatment (calcination) of kaolin, which is also used by the cement and concrete industry due to its latent hydraulic (pozzolanic) properties. Beside thermal activation, reactive materials can also be produced by mechanochemical activation in general. This paper deals with the mechanochemical activation of kaolin. The raw material was classified into various size fractions, then ground in a batch stirred media mill under varying circumstances (residence time, circumferential velocity). After grinding, the structural changes of the products were investigated by X-ray diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). In addition, the particle size distribution of the ground material was determined by laser scattering. As a result of the grinding experiments and analytical measurements of the products, it can be clearly seen that reactivity of kaolin can be improved significantly by mechanical activation in a stirred media mill, but due to its high energy density the circumstances were optimised carefully to avoid aggregation. Keywords: Kaolin, grinding, stirred media mill, mechanical activation, material structure

Jan 1, 2020

By K. Wu, X. Yuan, R. Du, C. Chao

"Lump coals are currently employed to replace part of coke in the COREX melter-gasifier for ironmaking. In order to optimize the process, the pyrolysis kinetics of Datong coal used in the COREX process was studied. A sectioning method is proposed to overcome certain shortcomings of traditional methods for studying the pyrolysis of coal. Based on the sectioning method and the characteristics of the coal pyrolysis process, the temperature range was divided into three intervals. In the first, the adsorbed gas and water of crystallization were removed; in the second, the coal was transformed into semi-coke; and finally, the semi-coke was further coked. Three models of reaction were then established to study the different stages of the pyrolysis process: an interfacial chemical reaction model, a random pore model, and internal diffusion with shrinking volume. The results showed that the experimental data fitted the models well, with all correlation coefficients (r2) exceeding 0.97. Finally, the mechanisms of reaction and kinetic parameters for each temperature range were derived, which laid a necessary foundation for optimizing the usage of non-coking coal in the COREX process. IntroductionIn view of environmental concerns and the shortage of good-quality coking coal, the COREX process was designed as a new ironmaking technology, attracting wide attention (Fang et al., 2005). In this process, lump coal and a small quantity of coke are directly charged into the melter-gasifier, where a high-quality reducing gas is generated for the reduction of the iron ore (Kumar et al., 2009). In contrast to the conventional blast furnace (BF) process, non-coking lump coal is used as the reducing agent and as the energy source, and the iron charge consists of lump ore and/or pellets, which results in the elimination of the coke oven and sintering plant as well as a decrease in investment (Kumar et al., 2009; Liu et al., 2012).Although the COREX process has made great progress, in current production practice the energy consumption greatly exceeds that of the BF, and it requires a certain amount of coke to maintain permeability of the semi-coke bed (Wang et al., 2008). In addition, the process consumes a lot of good-quality lump ore and lump coal. The pyrolysis of coal is the first step in most coal conversion processes, such as carbonization, gasification, and combustion (Aboyade et al., 2013). The reaction behaviour of lump coals in the COREX melter-gasifier is crucial, as it determines energy utilization and gas composition, as well as the metallurgical properties and particle size of the semi-coke produced (Prachethan et al., 2011; Zhang et al., 2014). In order to optimize the process and improve its competitiveness, the pyrolysis kinetics of Datong coal used in Baosteel’s COREX C-3000 facility was studied."

Jan 1, 2016

By N. V. Nemchinova, A. A. Kozlov, A. V. Epiforov

The gold dissolution in sulfuric acid media during industrial oxidative leaching test of sulfide gold-copper flotation concentrates has been achieved. The reason for this was using technological water containing thiocyanates and cyanides, which can dissolve gold under these conditions. The carbon in column (CIC) process for gold recovery from these solutions was proposed. However, significant amounts of copper and iron were adsorbed onto the carbon during CIC technology industrial tests. This resulted in a decrease of the gold content in the loaded carbon up to 0.5 kg/t. Further development of the technology was conducted by optimisation of gold and impurities stripping and implementation of carbon reactivation. It was shown, that the copper extraction from the loaded carbon during cyanide treatment was about 95%. The copper content in the stripped carbon after cyanide treatment was 1.76 kg/t. The gold recovery during high-pressure elution by caustic solution was 98%. The hydrochloric acidic treatment with thermal pre-treatment (reactivation) for removing iron and calcium from gold-free carbon was proposed. In this case, the iron and calcium extractions from carbon were 40-45 and 50-55% respectively. These tests showed that for carbon recycling the sequence operations of ‘cyanide treatment, gold elution, thermal pre-treatment, hydrochloric acidic treatment’ can be used. Keywords: Thiocyanate leaching, recovery of gold, carbon adsorption, gold elution, copper stripping, thermal reactivation of carbon, activated carbon, carbon-in-column

Jan 1, 2020

By X. Cao, R. Wang, H. Han, Y. Hu, Z. Wei, W. Sun, H. Tang, J. Wang

Flotation reagents play a vital role in mineral flotation. In the past century, most studies focused on the modification of anion or cation collectors and the synergistic effect of mixed collectors, which have contributed to research. In this study, we reviewed brand-new reagents, metal-organic/inorganic complexes, with the functional group of metal ion, which are totally different from the traditional anion or cation collector and show absolute specificity for some minerals. For example, Pb-BHA complex collector was developed to realise the atmospheric flotation of scheelite due to the absolute specificity for calcium minerals. Calcium oleate collector was found to be the effective species in the flotation of calcium minerals, and has been employed to selectively separate fluorite from calcite. Selective adsorption of Al-Na2SiO3 polymer on calcite surfaces proved the self-assembly of H2SiO3 polymer using Al3+ had stronger selectively adsorption ability than Na2SiO3. Also that Fe3+-starch complex was a better depressant for iron minerals than caustic starch and contributed to a more efficient reverse flotation. In conclusion, metal ions are good templates for molecular assembly and can be used to control the structure of metal complexes and exhibit special properties, which provide possibilities for the design of new flotation agents. Keywords: Metal-organic/inorganic; flotation; collector; depressant

Jan 1, 2020

By G. Sánchez, S. Seiler, B. Klein, T. Cebeci, P. Bradshaw

The Decar Nickel District is a greenfield discovery by FPX Nickel Corp., of nickel mineralisation located in central British Columbia (BC), Canada. The Baptiste deposit is part of the Decar Nickel District and is a unique deposit containing a nickel-iron alloy mineral called awaruite, with over 2-billion tonnes of inferred resource grading 0.12% Davis Tube Recoverable (DTR) nickel. This deposit represents a significant nickel resource. Awaruite is a high density and ferromagnetic mineral, which could be recovered, along with magnetite that is also present in the samples, using magnetic separation. However, there is still a lack of understanding of the properties of the awaruite and its metallurgical response. This information is imperative for the set-up of the variables involved in its concentration. The aim of this paper is to show and discuss the effect of magnetic field strength for the recovery of nickel from Baptiste deposit samples. Magnetic separation at bench and pilot scale with different magnetic field strengths is evaluated as a concentration method for awaruite. Mineralogical information is provided to support the results and also to briefly assess the variability of DTR nickel within the deposit. The Baptiste deposit is unique and will benefit from a sound scientific understanding of the process solution as well as other ongoing work. If successful, the outcome will lead to the development of a mine. With greater than 2-billion tonnes of inferred resource, the mine would represent a significant new source of nickel globally. Keywords: Nickel ore processing, magnetic separation , awaruite, magnetite

Jan 1, 2020

[Council for 1993/94 President Dr H. Scott-Russell President Elect J.A. Cruise Vice Presidents Senior D.A.J. Ross-Watt Junior P.D.K. Robinson Immediate Past President J.P. Hoffman Honorary Treasurer J.A. Cruise]

Jan 1, 1994

By N. Duda, P. Śliwiński, P. Stefaniak, B. Jachnik

Ventilation and air-conditioning are some of the most energy-consuming processes in deep underground mining. Additionally, the energy consumption of these processes systematically increases along with the expansion of the mine. Therefore, proper energy efficiency assessment and consumption forecasts of these systems are particularly important in modern mines for ongoing tracking and planning of the likely costs. In the article, a short-term prediction model for surface air–conditioning stations is described. This model takes into account dependencies that were identified, based on the data from the supervisory control and data acquisition (SCADA) systems. These dependencies between the response value and the external conditions are then incorporated into the model. This way, for example, the ambient temperature or the total number of specific days of the week (with sometimes significantly lower or higher than the weekly average energy consumption levels) are included. Taking into account these dependencies, and e.g. forecasted average monthly temperatures allow us to include the seasonality of energy consumption in the presented model. In the article, a sample energy efficiency analysis of the A/C system based on an example of the KGHM Polish Copper Polkowice-Sieroszowice mine is performed. The results of the solution proposed in the article are then evaluated, and compared to the currently functioning, more basic forecasting methods. However, given the general nature of the dependencies used in the model, similar solutions could be used in other case studies.

Sep 1, 2021

By J. O. Roux

The Impala Platinum Limited Base Metals Refinery in Springs, South Africa, refines convertor matte containing base metals and PGM?s (platinum group metals) using a hydrometallurgical process. In addition to a PGM-rich concentrate that is further refined, the Base Metals Refinery produces nickel (in powder or briquette form), copper cathodes and cobalt powder. Five leaching stages are utilized to remove the base metals and impurities from the PGM concentrate. The project described in this paper involves a radical redesign of the second stage leach autoclave with the aim of reducing maintenance costs and downtime, increasing throughput and ensuring a safer working environment. The second stage leach process at the Base Metals Refinery, produces a PGM-rich residue through the extraction of copper and any remaining base metals from the first stage leach solid residue material. Leaching is performed in an autoclave operating at a pressure of 600 kPaG and a temperature of 140°C to 150°C. Concentrated H2SO4 is added to the feed to produce a solution with a free acid content between 10 and 30 g/L and a pH of less than 2. Oxygen is passed into the 1st and 2nd compartments of the autoclave. As a result of the aggressive, highly oxidizing conditions within the autoclave, the original design utilized a heavy wall carbon steel shell with lead lining and two layers of acid bricks. The bricks acted as a wear resistant material and ensured a low surface temperature at the skin of the lead lining, whereas the lead lining acted as a corrosion barrier to protect the steel shell. These brick lined autoclaves were heavy, maintenance intensive and prone to catastrophic failure. A radical autoclave redesign was needed to reduce the high costs of manufacturing, installation and operation. Finite element modelling was used to optimize the design and various high alloy materials were investigated for the application. Based on extensive test work, the carbon steel shell was replaced with duplex SAF 2205 stainless steel in the new design. The use of this highly corrosion resistant material, eliminates the need for the lead and brick linings and reduces the wall thickness requirements substantially, resulting in an increase in the available volume for the same external shell dimensions. The vessel is welded in circular sections to form an elongated, impermeable, cylindrical body, with several agitator nozzles and compartments. The first new duplex stainless steel unit has been in continuous operation for more than 24 months and its performance has exceeded the highest expectations. The design was so successful that a patent has been registered. The major benefits of the new stainless steel design include increased throughput, improved performance, less downtime and a safer working environment. Lead has been eliminated and replaced with a more environmentally safe material, and the total lifespan of the vessel has been extended. In addition, the autoclave project has made significant developments in advancing the field of welding and optimizing the integrity of welding quality standards in South Africa.

Jan 1, 2009

By F. D. Agrensa, J. Hadjigeorgiou, E. Storimans, S. J. Thorpe

Reinforcement and surface support are part of an integrated system that transfers and shares loaduntil the excavation surface is stabilized or until the ground support system fails. Steel mesh is the most popular primary surface support element in underground hard rock mines in Canada. Mesh straps are a secondary surface support that provide additional containment as they distribute the load between and across the reinforcement elements. This investigation addresses the role of steel properties, and in particular steel chemistry, in the long-term performance of mesh and mesh straps when exposed to an aggressive corrosive environment. It reports on comparative accelerated corrosion studies to compare the resistance to corrosion of different surface support elements. This has significant implications on the choice of surface support and the anticipated rehabilitation requirements.

Oct 9, 2024

By B. D. H. Knights

In November 2009 Mintek installed the FloatStar? advanced flotation stabilization system on Vale's Cauê iron ore beneficiation plant in Brazil. In September 2010 the system was upgraded to include flotation optimization. The circuit consisted of two parallel cleaner circuits producing final concentrate. The tailings from the cleaner section passed through a scavenger circuit. Large, well-instrumented feed sumps played an important role in circuit stability, presenting a good opportunity for advanced control. Previously the plant was controlled using distributed control system (DCS) level control only. The flotation circuit processes roughly 30kt/day. The FloatStar system provided advanced control of the flotation circuit as well as of the sumps feeding the circuit. The system underwent a lengthy trial to assess the benefit that it provided. Two data sets were analysed, showing performance under advanced stabilization and optimization respectively. Several validation and consistency criteria were employed to ensure the quality of the analysis. Iron recovery and iron tailings grade were used to measure system performance. The analysis showed that the system increased recovery by up to 2.7%. In addition, the system decreased the iron tailings grade by between 1.2% (from 23.5% to 22.3%) and 4.3% (from 31.3% to 27.0%) during different test campaigns. The analysis also showed that the entire FloatStar stabilization system was active for 72.7% of the time from first activation to the end of the first data set (approximately 200 days). From the analysis it was concluded that under similar conditions for 'ON' and 'OFF' tests, the system provides a clear benefit. It was also found that over the longer term, the system continues to provide a benefit. This finding suggests that the results were not simply due to a short-term advantage. The size of the data set, as well as the magnitude of the recovery improvements, lends considerable confidence to these results. Therefore, it can be concluded that the FloatStar control system provides substantial benefit to operations at this site.

Jan 1, 2012

By N. Naude, W. P. Roux, O. Kaba

Ceramic filtration plates are used for dewatering slurries with high solid concentrations and particles in the size range of 30 μm to 150 μm. After extensive operating times, the ceramic filter plates at Minas Rio in Brazil begin to blind due to the precipitation of barium sulphate on the surface of the ceramic filter plate, which reduces the overall efficiency of the filtration process. Further research is needed to identify the barium precipitate phases on the blocked filter plates and its thermodynamic and kinetic behaviour in the system. A crystallography analysis was performed on the sample and the results showed that there are two different sets of precipitates formed on the filter plate: grey crystals which were large and scatted on the filter plate and red micro crystals that covered the entire surface of the filter plate. The red microcrystals on the sample were identified with XRD, which indicated that the sample contained barium sulphate in the mineral form barite. Experiments were conducted to determine the optimum conditions under which barium precipitation will occur. The conditions tested as a possible driving force for barium sulphate precipitation were the effect of temperature, pH and concentration. The pH and temperature ranges were pushed to both the lower and higher boundaries. The effect of temperatures as low as 15oC was studied and pH levels of 7 and upwards. The first nuclei started appearing at a pH of 7 but significant growth is promoted at higher pH levels. The X-Ray diffraction analysis confirmed the phase of the precipitates formed, and the orthorhombic crystallographic structure formed is a characteristic of barium sulphate. Keywords: Iron ore, barium sulphate, temperature, pH, concentration, morphology, and ceramic filter plate

Jan 1, 2020

A Colloquium and General Meeting were held on 17th March 1971, the theme being 'Future trends in steel production'. Mr V. C. Robinson (President) was in the Chair. The Colloquium was attended by 121 delegates and was opened by the President at 10 a.m. OBITUARIES THE PRESIDENT: 'It is my sad duty to announce the death of the following: F. O. Read, Fellow, who joined the Institute in 1957 and passed away on 13th January, 1971. P. G. M. May, Member, who joined the Institute in 1969 and passed away on 10th August, 1970. R. J. J. Rademeyer, Life Fellow, who joined the Institute in 1942 and passed away on 23rd September, 1970. As a mark of respect to the memory of the deceased and in sympathy with the bereaved I would ask you all to rise and observe a few moments silence. CONFIRMATION OF MINUTES THE PRESIDENT: 'May we confirm the minutes of the monthly general meeting held on 21st October and 18th November, 1970, as published in the Journal'. Agreed. MEMBERSHIP THE PRESIDENT: 'I have much pleasure in announcing that the names of the undermentioned candidates, having been published in accordance with ByLaw 5.2.2, Council has elected them to membership of the Institute in the following grades: FELLOWS: Romain August Lathioor, Paolo Piga, Renato Ribacchi, Willem Frederick Jacobus Smith, Matthew Churchill, Thomas Anthony James Braithwaite, Hugh Patrick Hart, Eleanor Innocentius Muller, David Alton Smith. MEMBERS: Douglas Adendorff, Petrus Jacob du Plooy, James Valentine Grant Middleton, Karl Anders Ullerstam, Josephus Theodorus Johannes van Wyk, Frank Douglas Abbott. GRADUATES: David Mervyn Gilbart-Smith, John Philip Wilcocks Bennie, Hendrik Theunis Burger, Johann Wilhelm Coetzee, Johannes Stephanus StOols, Leon van Tonder, Brian George Harvey, John Kennedy McLean. ASSOCIATES Richard Cyril Lee Stoyell, Terrence Brian Gouws, Alister Rodney Frederick MacDonald. STUDENTS: Andries Groenewald, Christiaan Johannes Hattingh, William Hendrik Hofmeyr, Stanley Thomas Vincent. I welcome the new members to the Institute and congratulate them on their election. COLLOQUIUM The President welcomed everyone present and mentioned that this was the first of the Colloquia which are to replace the Institute's monthly meetings. He stressed that discussion at Colloquia would be completely informal and would not be recorded unless the contributor requested publication. In conclusion, he thanked the organising committee, the authors and the contributors, and introduced the author of the first paper. The following papers were presented:- 'The future development of the Iron and Steel Industry' by J. P. Coetzee (Published in the Journal March 1971). Among those who contributed to the paper were Dr Bleloch, Dr K. Gebhard, Dr Way and Professor Müller. The main point made by Dr Bleloch related to the reserves of coking coal and of coal for power generation this in country and he deduced that in South Africa we are critically short of coking coal. On the basis that 4 million tons per year of coking coal are consumed for our present steel production, over 16 million tons would be required to meet the anticipated expansion in steel output by A.D. 2000. This must be set against the grim forecast made by the Coal Advisory Board in 1967 that our national reserves of coking coal will be exhausted before A.D. 2000. This gives tremendous significance to the development work presently being carried out by Iscor on alternative methods for coke production. On the other hand the blast furnace may have to be replaced by an alternative process for the reduction of iron ores, e.g., the use of rotary kilns followed by electric arc smelting. Dr Bleloch also expressed grave forebodings about the reserves of bituminous coal, pointing out that with present methods of mining the recoverable coal in any given reserve is in general only 50 per cent of that reserve. He stated that in the past seventy years great quantities of coal have been forever placed beyond the reach of mining by being undermined by extraction of lower seams or lost by being burned. A final point made by Dr Bleloch was the fast rise in the capital investment in a fully integrated steel plant, the figure having risen in the past decade from just over R200 to R350 per ton of finished steel per annum. Dr Gebhard spoke of the direct reduction processes for iron making pointing out the difficulties of securing a high percentage of reduction and the relatively high cost of smelting in electric arc furnaces. As an alternative he suggested briquetting the high carbon sponge iron

By J. Bal, V. D. Dao, W. Li

"SynopsisThis study proposes a methodology for evaluating the risk of coal bumps in multiple-seam longwall mining. Both the stress field and the total energy release (TER) during retreat were evaluated in the specified case involving multiple-seam mining using the LaModel program. The results of numerical simulations indicated that both the peak vertical stresses on the panel edges and the peak TERs in the outby longwalls increased significantly as the horizontal offsets were reduced from 60 m to zero. With the comprehensive consideration of the stress field and TERs, a conservative offset of 60 m was ultimately adopted when developing the gateroads of the lower panel in the field. The field measurements indicated that coal bumps were avoided completely by employing the proposed design, and the maximum roof-to-floor and rib-to-rib convergences of the tailgate during retreat were only 360 mm and 576 mm, respectively.IntroductionCoal bumps – sudden, violent bursts of coal – pose a serious threat to the safe excavation of coal. Their occurrence depends on the properties of the surrounding rocks, stress field, and dynamic disturbance. The complexity of the mechanism of coal bumps is further enhanced in multiple-seam mining due to seam interaction. Multiple-seam mining is most frequently found in the coalfields in eastern China, such as Xuzhou, Xinwen, Zaozhuang, and Huainan. In the past, due to issues of availability, economics, and ignorance of the potential risk in multipleseam mining, coal seams in such conditions were mined without proper planning to account for seam interaction. Fortunately, studies published over the past three decades have raised awareness of the problems associated with multiple-seam mining, and indicated that the ground control issues induced by multiple-seam mining can be avoided and/or minimized with proper planning.A number of technical studies pertaining to the design of multiple-seam mines have been published. These studies can be divided into two groups based on their methodologies of design: empirical (Chekan and Listak, 1993; Haycocks and Zhou, 1990, Matetic et al.; 1987a, 1987b) and numerical approaches (Li et al., 2000; Maleki, 2007; Mark, 2007; Peng, 2007; Zipf, 2005). The majority of the extant studies on the interaction mechanisms in multiple-seam mining have focused on the load transfer during operation, resulting in the proposal of the pressure bulb theory (Forrest et al., 1987; Haycocks and Karmis, 1983; Peng, 2008; Peng and Chandra, 1980) and pressure arch theory (Holland, 1973; Oram and Ponder, 1997) to guide multiple-seam mine design. However, neither, of these theories can be used to evaluate the potential for coal bumps."

Jan 1, 2015

Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mechanical properties. In this paper, mechanical properties and slake durability tests for weak and clay-bearing rocks from Beypazari Trona Bed in Ankara, were performed in order to assess the slake durability and mechanical properties (especially rock strength) of these rocks as well as to understand the relationship between mechanical properties and slake durability. In performing this relationship, statistical based correlation has been applied.

Jan 1, 2003

By D. D. Aksenova, V. A. Ignatkina, L. A. Samatova, A. V. Lygach, E. D. Shepeta

Calcium minerals such as scheelite, phosphate, apatite are valuable minerals, which have similar flotation properties to the calcium gangue minerals. An additional problem is the fine dispersion and close mineral association of valuable and other minerals. Low polar compounds (non-ionic surfactant), such as fatty iso alcohols, neonol and phosphol, and their combinations with sodium oleate have been studied using flotation of monominerals and ore flotation; ATR IR spectroscopy and TEM for study surface of minerals; UV spectroscopy for control solubility, aggregation and de-aggregation processes. Increase in solubility of fatty acid collectors was confirmed by low soluble (heteropolar) compounds. Oxyethylated esters of phosphoric acid are adsorbed on phosphorite by -O2PO2R2 and on other rock minerals by donation of OH bond. Same effect shows difference of adsorption of fatty iso alcohols on calcite and scheelite. The different forms of adsorption of ionic and nonionic compound on a sparingly-soluble mineral surface creates distinction of the flotation kinetics and technological balance of ore flotation. The results of the separation of flotation of scheelite from calcite depend on the order of pouring into pulp of fatty iso alcohols and oleate, and their ratio in the mixture. Increasing scheelite recovery into rougher scheelite concentrate by 3.6% for both the flotation and sludge classes was obtained. Calcite recovery varied slightly upwards or downwards by 0.8-2.4%. The use of the non-ionic surfactant phosphol in combination with a fatty acid soap allows for obtaining a phosphate concentrate with more than 28% P2O5 content and almost 80% recovery in flotation operation. It is not obtainable with other reagent regimes. Keywords: Flotation, calcium minerals, oleate, fatty isoalcols, neonol, oxyethylated esters, adsorption

Jan 1, 2020

By T. M. Chagwedera, A. E. Lewis, J. Chivavava

Eutectic freeze crystallisation is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates, which are often a mixture of different inorganic salts. The treatment of calcium sulphate-rich brine solutions through eutectic freeze crystallisation has resulted in gypsum scale formation on the walls of the crystallisers and ancillary equipment. In order to prevent gypsum scaling on equipment surfaces, it is essential to understand the mechanism of gypsum scaling on cold surfaces. This paper focused on the interaction between gypsum crystallisation in the bulk solution and scaling on the crystalliser walls in the presence of gypsum seeds. A cooled, U-shaped stainless-steel tube suspended in the saturated solution was employed as the scaling surface. Preliminary results showed that the scale layer was predominantly composed of needle-type and hexagonal prismatic crystals. The rate of scale deposition was highest during the first 24 hours, thereafter it decreased. A thin scale layer was observed to have coated the tube within the first hour of the experiment. Seeding, using reagent grade gypsum crystals, was effective in reducing scale layer formation through providing a surface for growth. The highest scale reduction, 81%, was realised at a seed loading of 0.50 g/L. At a high seed loading of 4.01 g/L, the seed material adhered to the tube. Keywords: Gypsum, eutectic freeze crystallization, seeding, scaling, cooling crystallisation

Jan 1, 2020

By E. Marè, D. R. Groot, R. Engelbrecht, T. Coetsee

Hydrogen peroxide is often used as an oxidising agent in experimental waste electronic equipment (WEE) leaching work. However, the high cost of peroxide is a negative factor in its consideration in further process development. A few studies have reported on the efficient application of peroxide addition schedules to ensure optimum reagent consumption. Large quantities of unleached substrate material contained in WEE feed material result in a large dead volume of material in the leaching reactor. This factor necessitates fast reaction rates to enable the use of a high feed material throughput reactor to enhance overall project viability via hydrometallurgical processing. In this study the effects of hydrogen peroxide addition schedules on base metal leaching efficiency and solution temperatures were tested at laboratory scale. The results showed that overall peroxide consumption can be optimised to lower levels by matching peroxide additions to the particular feed material’s leaching behaviour. A simplified integrated model for peroxide decomposition is used to explain its effect on solution temperatures and leaching rates. Keywords: Peroxide consumption, waste electronic equipment, copper leaching, integrated model

Jan 1, 2020