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By Z. L. Xue, J. L. Li, X. Y. Wang

"In low-carbon energy-efficient basic oxygen furnace (BOF) steelmaking processes, limestone partly or completely replaces the active lime. The effects of limestone calcination temperature (1200–1500°C) and time (5–15 minutes) on lime reactivity and CaO grain size were investigated. The reactivity was evaluated by titration with hydrochloric acid, and the CaO grain size was analysed using scanning electron microscopy. The results revealed that for calcination temperatures higher than 1300°C, the reactivity reached a maximum and then decreased . The higher the temperature, the earlier the peak of reactivity appears. The CaO grains grow with increasing temperature and time, which leads to the decrease of reactivity. Notably, the effects of temperature on CaO grain size and reactivity are more marked than that of time. To obtain active lime calcined at ultra-high temperature by flash heating, the calcination conditions should be 1300–1400°C for 10–15 minutes, or 1400–1500°C for 8–10 minutes. IntroductionLime is one of the most important slag-making materials for dephosphorization and desulphurization in the basic oxygen furnace (BOF) steelmaking process. The reactivity of lime is a measure of its capability to take part in slag-making. Lime having a reactivity of more than 300.0 mL (4 N HCl), determined by hydrochloric acid titration is generally referred to as active lime (Rusjan et al., 2007; Zeman, 2008). At present, the active lime used for BOF processes comes primarily from a kiln or shaft kiln, where limestone is preheated at 700– 900°C, and then calcined at 1050–1200°C (Drenhaus et al., 2010; Oates, 2007)."

Jan 1, 2016

By G. R. Lane

My opportunity to serve as President of the prestigious Southern African Institute of Mining and Metallurgy (SAIMM) was made possible by an Anglo American scholarship 39 years ago—a pivotal moment that set me on a career path spanning various roles and start-up ventures in the mining industry. Over the past decade, I have been privileged to broaden my experience by consulting across diverse industries globally. This exposure revealed something profound: what I had previously considered mining-specific challenges are, in fact, universal across many sectors. At its core, a mining operation is a complex system of interconnected activities—from exploration through mining operations like drill and blast, load and haul, to beneficiation, and outbound logistics. My cross-industry work has clearly shown that diverse sectors, such as chocolate manufacturing, tissue paper production, toilet paper converting facilities, labgrown diamonds, or high-tech equipment lifecycle management, all rely on value streams of interconnected activities to transform products. The objective is to maximise throughput while effectively managing performance variability. The primary difference lies solely in the specific technical expertise required for each industry, such as chemical, mining, processing, or metallurgical engineering. Across all these industries, I have observed a consistent pattern, that is, performance is primarily driven by individual efforts, where people react and work diligently as situations unfold in real-time. General managers and their teams often operate tactically, focusing on explaining yesterday’s poor performance rather than proactively setting up operations for success. This often resembles an ‘‘under-7s soccer match’’, with everyone chasing the ball. The common response to issues is to add more ad hoc meetings. This effort-driven organisational behaviour persists regardless of whether operations are greenfield digital manufacturing facilities, advanced digital mines with advanced process control, or operations run on paper and Excel spreadsheets for data acquisition. Paradoxically, more real-time data can lead to increased data noise, greater indecision, and sometimes, lower performance. Despite value streams often operating significantly below capacity, organisations continue to invest heavily in additional equipment or in ‘‘glossy brochure promises’’ of Industry 4.0 digital technology and real-time data solutions, which frequently fail to deliver value. This leads to a critical question: Have we underinvested in our most valuable resource— people? Even Tesla faced this challenge with their underperforming fully automated Model X facility. We must shift our focus to designing the ecosystem, or operating model, of our organisations. This extends beyond the traditional triad of people, process, and technology, and moves beyond simplistic views of change management. Artificial Intelligence (AI) has the potential to add significant value, but it also introduces another layer of complexity into designing the organisation of the future. My full presidential address below at the SAIMM AGM discussed the symptoms of an effort-driven organisation and covered the fundamental building blocks and requirements of an operating model, including recommendations on implementing a people-centric approach.

Oct 2, 2025

By A. F. Silva, R. Dockendorff, J. M. Girao Sotomayor, V. F. Navarro Torres, C. Castro

This paper shows the importance of performing probabilistic analyses in open pits, especially for mine planning, which can lead to more efficient ore extraction and meeting the acceptability criteria for safety in mine slopes. Three-dimensional stability analyses were performed to evaluate the future geometry of a large open pit for iron ore extraction in Brazil. The strength parameters of the lithologies were calibrated using ruptures in the pit walls. After determining the factors of safety (FoSs) from the calibrated parameters, probabilistic analyses were performed using the total range of values of each parameter under different field conditions to verify the reliability of the initial analysis. In this sense, it was possible to plot the probability of failure (PoF) and the FoS on the graph of slope height versus slope interramp angle (IRA) for the future pit in each lithology. IRA recommendations are made for two scenarios: (1) the best scenario: dry without ubiquitous joints and (2) the worst scenario: the water table at 10 m depth with ubiquitous joints in the most unfavourable direction. The results show that probabilistic evaluation is an important tool for establishing alert mechanisms in slopes that can be termed stable.

Jul 2, 2022

By E. Mokgwamme, T. Goff, M. Mvalelwa, P. Spratt, P. Bezuidenhout, P. Nkosi, H. Joubert, G. de Villiers

Sibanye-Stillwater recently completed a partial sidewall rebuild on Furnace 1 at its Marikana smelter complex. The project involved matte taphole maintenance, which required the removal and subsequent replacement of 18 composite copper-graphite coolers and a section of the lower refractory sidewall. These composite copper-graphite coolers are a newly developed cooling design by Tenova Pyromet, and this rebuild project provided valuable insight into the performance of the composite coolers. The novel composite cooler design was implemented to serve as a safeguard against localised wear and corrosion in the furnace sidewall, particularly at the slag-concentrate interface, where chloride-accelerated sulphidation has been identified as a dominant degradation mechanism affecting the copper cooling elements. The composite cooler design is unique in that all the exposed sides of the water-cooled copper elements are fully encapsulated in graphite, which protects the copper from corrosive sulphur- and chlorinebearing gases and condensates. This sidewall cooling system was designed to improve corrosion resistance, stabilise freeze lining formation, and extend the campaign life of the furnace sidewall. The partial sidewall rebuild was executed during a planned maintenance shutdown with the main objective of replacing the matte taphole lintel bricks. This paper serves as a case study that compares and evaluates the operational performance of the composite coolers before and after the rebuild. The installation method is discussed to highlight the approach taken to ensure a sound installation while minimising downtime, as well as to present some lessons learned in the process.

Mar 6, 2026

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 H. J. R. Way

Dr H. J. R. Way: In his reply to my queries Mr Bath still adheres to his statement that it may be possible to replace the estimated R200 million reduction in gold revenue in 1980 by exports of ferro-chromium, and apparently based his conclusion on a growth rate in demand for corrosion resistant steels of 10 per cent per annum in the next few years. As I pointed out at the previous discussion at Middelburg this would entail a production of about one million tons of ferro-chromium in 1980. Exact statistics of South African ferro-chromium production are not available, a fact which is very much to be regretted. But statistics of exports of ferro-chromium are available from "Foreign Trade Statistics" of the Customs and Excise. These show that South Africa exported 99,580 short tons in 1967. The quantity of ferro-chromium consumed in South Africa in 1967 was fairly small and we can therefore assume that the production was 99,580 tons. For this amount to grow to 1,000,000 tons in 1980 would require a growth rate of 19.4 per cent per annum. At 10 per cent this would grow to 344,000 tons and at 7 per cent 240,000 tons. The following growth rates in the form of average trends are pertinent: STEEL - Per annum World steel ingot production - 1957-67 – 6.8 per cent Free-world ingot production - 1957-67 – 6.0 per cent Consumptions of crude steel by four major Free-world Consumers - 1957-67 - 5.6 per cent CHROMITE World production - 1952-67 - 2.5 per cent South African total sales - 1948-67 – 5.4 per cent South African exports - 1948-67 – 3.9 per cent United States consumption, very irregular, but - 1962-67 – 6.5 per cent FERRO-CHROMIUM - Per annum United States consumption - 1952-67 - 6.5 per cent South African exports - 1957-62 - 25.2 per cent South African exports - 1962-66 - 41.9 per cent South African exports - 1966-68 - 21.2 per cent These figures show that exports of ferro-chromium have been growing at a very high rate varying from 21.2 per cent to 41.9 per cent since 1957, but in view of the market situation it seems somewhat doubtful if that high rate can be maintained up to 1980. Of our 1966 exports U.S.A. took 63 per cent which was 53 per cent of their total imports. Their average consumption is trending at a growth rate of 6.5 per cent per annum from 1952-67, but the growth from 1964-66 was 5- 2 per cent and 1966-67, -12 per cent!

Mar 1, 1968

By T. M. Louw, L. Auret, S. M. Bradshaw, F. F. Noelle

Modern industrial processes undergo frequent process state shifts due to changes in demand, feedstock or maintenance operations. Multimodal continuous process monitoring is therefore required for effective plant operation. Steady state analysis is a key component in effective multimodal monitoring. Various issues still remain in determining the starting and ending times of transition states. High dimensionality of process data is a characteristic that makes it difficult to select variables to consider when conducting steady state analysis. In order to address these problems, steady state detection on the principal component space is proposed. First, data undergoes principle component analysis to reduce dimensionality, then existing multivariate steady state detection algorithms are applied on the principle component scores. A novel algorithm, threshold PCA-SSD, is proposed and compared to an existing technique for steady state detection. The algorithms are investigated on high dimensional synthetic data Keywords: Multimode process, steady state detection, principle component analysis

Jan 1, 2020

By T. Matlou, S. Myendeki, V. Midzi, T. Zulu, H. Mabotja, T. Mulabisana, B. S. Zulu, L. Hlatshwayo, T. Makhateng

The Council for Geoscience (CGS) performed a macroseismic investigation following the occurrence of an earthquake in the Boksburg area on 11 June 2023. The event had a magnitude of ML 4.4 and a focal mechanism that showed the event as having strike-slip motion along a northwest-southeast oriented fault. The event resulted in aftershocks, some of which occurred away from the causative fault in the east in an area without a mapped fault. However, the cluster of past events in that area suggests that there is an active fault. Due to the size of the main earthquake, a macroseismic survey was conducted to determine its impact on the community in the region. Analysis of observed data obtained from questionnaires resulted in the creation of 153 intensity data points. Their distribution showed high intensity values close to the earthquake source area. However, the investigation highlighted a number of anomalies, such as the higher than expected intensity values observed far from the event epicentre. It could be that these anomalies are caused by site conditions, for example, amplification of ground motion due to thick soil layers.

Jan 12, 2025

By L. von Ketelhodt

Dual energy X-ray transmission (DE-XRT) sorting is a recent development in the range of sensor-based sorting technologies available today. DE-XRT is particularly suitable for dry coarse coal beneficiation in the size range -120 mm +12 mm. In this paper, we describe the technology and show the results of a number of test runs conducted on different types of coal from the USA and South Africa. The results have shown that DE-XRT is an effective technology not only for deshaling of coal and removing pyritic sulphur but also for separating coal and torbanite. The use of dry deshaling methods will be more important as water availability becomes a greater concern. DE-XRT is one such technology which will be incorporated in future dry coal processing plants.

Jan 1, 2010

By F. Dong, F. Yang, J. Wang, Z. Wang, D. Mingxia

Antimony oxide ores are important antimony resources, but their recovery is still a problem. In this paper, the adsorption behaviour and mechanism of dodecamine and quaternary ammonium salt on the surface of cervantite and quartz were investigated. The flotation behaviour of cervantite and quartz using quaternary ammonium salts and dodecylamine as collectors was studied by single mineral flotation experiments. The adsorbed amount was measured and infrared spectroscopy was used to study the ability of several cationic collectors to float cervantite and quartz. The results show that quaternary ammonium salts can simultaneously float the cervantite and quartz. It is difficult to achieve separation of the two minerals using quaternary ammonium salts as collectors. At pH>10, dodecylamine can float quartz but not cervantite, which can achieve reverse flotation separation of the two minerals. The difference between the abilities of quaternary ammonium salts and dodecylamine to float cervantite and quartz lies in the different ionisation properties of the two reagents. Quaternary ammonium salt is a strong electrolyte that is completely ionised in the pulp and exists mainly in the form of quaternary ammonium ions. Dodecylamine is a weak electrolyte and predominantly forms molecules under alkaline conditions. Keywords: Cervantite, quartz, dodecylamine, quaternary ammonium salts, flotation

Jan 1, 2020

Grains are subject to contamination by mycotoxins which are metabolic by-products of various fungi. The fungal infestations produce local concentrations of the mycotoxins thousands of times higher than the average. These facts make the sampling of the grain for assessment of the mean mycotoxin levels potentially very difficult. In the context of sampling theory, this morphology of the infestations creates a very high distributional and intrinsic heterogeneity of the grain shipment. The distributions of mycotoxin concentrations in seaborne shipments that exist at loading and the number and intensity of infestations that develop under shipping conditions are unknown. All grain shipments carry spores that may give rise to mycotoxin-producing colonies; moisture and temperature determine the final extent of the problem. This paper develops the value of the sampling constant with respect to intrinsic heterogeneity based on data on observed Ochratoxin A (OTA) concentrations in individual wheat kernels. A useful relationship between the distribution of mycotoxin concentrations on a kernel to kernel basis and the distribution of concentration over subsamples is developed.

Jan 1, 2009

By B. Talbot

How this simple plant generates a large revenue stream. The concept behind the Tailings Scavenging Plant (TSP) is simple: it is a non-complicated modular plant which is designed to be more stable than upstream plants. This, plus the use of ?high energy?, enables the plant to recover any metal missed by the upstream operation. Impala Platinum?Mineral process started pilot plant exercises in June 2003. The pilot plant ran for one year before the capital for the full-scale plant was approved. This year was used to motivate, design and cost a full-scale plant. The metal produced during the pilot and feasibility study enabled this part of the project to run at a small profit. The scale-up to full-scale was relatively simple as the pilot plant had a capacity of 180 m3/hrand the full-scale plant was designed for a capacity of 550 m3/h. The design for the full scale plant was completed in May 2003, with ground breaking taking place on 19 May 2003. The construction phase of the project went well with the commissioning of the first two modules taking place on 22 October 2003. The remaining two modules were commissioned two weeks later. The plant was at full capacity by the 20 November 2003. A review of the plants performance for the first 5 production months is as follows: the plant has required only a few minor modifications and additions, it has run well in excess of 95%availability with no major wear apparent. In addition to this, the plant has produced 3 times the metal forecast.

Jan 1, 2004

By P. J. Bartlett, H. A. D. Kirsten

A two-dimensional numerical scheme for the simulation of the plastic stress-strain properties of rock, and the various components of rock reinforcement and shotcrete, was used to rigorously determine the characteristics of tunnel support under squeezing conditions. D-shaped tunnels varying in size from 2,8 to 6,5 m in height and width were considered. The four main mining stages in the BAS block cave on Premier Mine were simulated as alternative sets of field stresses. The rock reinforcement comprised 1,8 m long fully grouted rockbolts and 6,0 m long fully grouted cable anchors at various spacings, and of various tensile and bond strengths. Various thicknesses of shotcrete and footwall support configurations were also considered. It was found that shotcrete and rock reinforcement, owing to inherent differences in stiffness, do not function in unison. As monolithic application, shotcrete has an overriding avidity for the imposed loading and destructs itself unless of extraordinary thickness. Under squeezing conditions, it accordingly supports the excavation surface while the rock reinforcement contains on-going convergence. The loads in the various support components can be determined only by simulation of the shotcrete as a stress-relieved medium to represent its broken condition in the field. The loads in the rock reinforcement vary around a tunnel and are the largest in the sidewalls. The loads increase with an increase in tunnel dimensions, the increase in load in the sidewall due to an increase in height being larger than that in the hanging- and footwalls due to an increase in width. Depending on the strength of the rock, the loads in the rock reinforcement become prohibitively large beyond a certain size of tunnel. The reinforcement of footwall rock can be omitted without adversely affecting that in other walls, provided the tensile and bond strengths of the reinforcement are not limited. The resulting footwall heave may, however, result in undermining of the reinforcement in the adjoining walls. A relative depth of anchor of 1,37 provides adequate bond strength in the larger sizes of tunnel, whereas, in smaller tunnels, anchor length is determined by the allowable convergence. The lack of fun column grouting adversely affects the efficiency of rock reinforcement to a major extent. The loads in rock reinforcement are very sensitive to the strength of the rock. Owing to a lack in refinement and calculational rigour, empirical classification systems are an inappropriate means for the design of tunnel support in squeezing conditions and, as a result, grossly unclear-estimate the support requirements.

Jan 1, 1992

By S. M. Brabyn

The wear in mild steel pipelines used to convey rod-milled waste backfill was determined and then compared with that obtained using a laboratory rig designed to simulate the wear condition in slurry pipelines. The relative importance of corrosion and abrasion was investigated under various conditions of water quality and particle size distribution. The laboratory rig was then used to evaluate other possible materials of construction for backfill pipelines. A preliminary assessment of the economic viability of pipelines made of alternative materials is included.

Jan 1, 1988

By D. J. Shields

The U.S. Bureau of Mines has developed a microcomputer-based mineral modelling system that enhances analytical capabilities of the agency. It draws upon the extensive data base previously developed for the Bureau's Availability studies. The model is first formulated as a generalized network flow optimization problem, the optimal flows from which are fed into a transportation algorithm. The goal of the modelling system is first to fulfill prespecified demand at the minimum opportunity cost and second to identify feasible, optimal trade patterns. The system facilitates the analysis of policy issues on a real-time basis and supports the Bureau's mission to assess mineral resources.

Jan 1, 1987

By M. R. Khalesi, Y. Kianinia, A. Seyedhakimi, F. Soltani

"The feed ore to Agh-Darreh gold processing plant (Takab City, Iran) contains 2 ppm Au, 7 ppm Ag, and 120 ppm Hg. After cyanide leaching of the feed at pH 10.4, 80% of the total mercury (in the form of cinnabar and metacinnabar) goes to the tailings dam. In this research, separation of mercury from the tailings by flotation was investigated. The effects of collector type and dosage, pH, and the number of cleaner stages were studied. The results showed that after two stages of cleaning a 40–62% recovery of Hg at a grade of 14.3% Hg is attainable. Recycle water from a test in which 50 g/t amyl xanthate and 30 g/t pine oil was used in the flotation stage showed no adverse effect on the leaching and adsorption of gold onto activated carbon.IntroductionMercury, most commonly found in the nature as the mineral cinnabar (HgS), is a hazardous substance because of its mobility and toxicity (Kyle et al., 2012). Roasting is the wellestablished treatment method for mercury ores, in which the sulphur is burned and volatilized and mercury recovered subsequently by cooling and condensation. However, for low-grade ores, flotation is mainly applied for primary concentration due to its comparatively low costs, low environmental hazards, and flexibility regarding feed variations (Bulatovic, 2007). Particularly, cinnabar can be easily recovered by flotation using pine oil and a collector such as xanthate (Bulatovic, 2007; Crozier, 1991). Floatability of cinnabar is reduced due to surface oxidation when it is exposed to the atmosphere after crushing. This problem can be eliminated by adding copper sulphate and lead nitrate or acetate. The best pH for cinnabar flotation is in the range of 6.5 to 8.5 according to Erspamer and Wells, (1954), who reported that cinnabar and stibnite can be floated with long-chain xanthate collectors and an alcohol frother, with cumulative recoveries of 97.8% and 94.7%, respectively. Lead acetate was used as an activator."

Jan 1, 2017

The Barrick North Mara Mine and the Advanced Systems Group at SGS Minerals collaborated on the implementation of a grinding expert system for the control and optimisation of a single semi autogenous (SAG) mill. Over the last 5 years, grinding expert control has gained wide acceptance by mineral processors. In this paper, two key factors for success are highlighted: the adaptability of the software tools and the interaction with site personnel. Created with SGS?s MET expert console (MEC) toolkit, and running on Gensym?s G2 real time inference software, the North Mara expert logic has been set up to keep a steady and on spec leaching feed slurry while striving to maximize throughput. Leach feed stability was achieved by standardizing operating practices across shifts; a result of successful collaboration with site personnel in developing a consistent control strategy. The strategy maintains the SAG load and power draw in an optimised range by manipulating SAG feed rates and inlet water flow. The project life-cycle was slightly longer than average due to site specific constraints. One of these was the high turnover rate of site?s workforce during the project, coupled with the availability of key staff on site due to the fly in fly out work roster. These constraints called for different, and innovative ways of project commissioning and hand-over. This paper describes details of the control solution, its implementation as well as results and conclusions.

Jan 1, 2009

By Thermo Electron, Tim Sennett

Summary ?SamStat Development ?SamStat Description ?Accuracy ?Availability ?Cost of ownership ?Capital ?Installation ?Operating/Maintenance ?Case Studies ?Modikwa ?Combined concentrate sampling ?Cerro Verde ?State of the art sampling & analysis ?Ok Tedi Final Tails ?brownfields installation ?Conclusion

Jan 1, 2005

By L. Shoke

The aim of this study was to develop an in-house tensile testing procedure that would yield accurate and reproducible parameters as input material properties into computational models for numerical simulations of the mechanical behaviour of TM380 mild steel. To achieve this objective, we reviewed the ISO 6892:2009 tensile testing standard along with reported good practice guidelines. Tensile tests were conducted on a dog-bone shaped TM380 mild steel specimen with strain gauges attached on either side, to monitor alignment and measure strain, using three different types of tensile testing machines. Parameters quantified included yield stress, ultimate tensile strength, and modulus of elasticity. The values of these parameters were found to be in agreement with the values supplied by the manufacturer's specification and showed minimal variations between laboratories. Thus it can be concluded that the tensile test procedure used resulted in accurate and reproducible results. The strain values calculated as per standard were in disagreement with those determined from extensometer and strain gauges and resulted in lower elastic modulus values. This confirms that the current testing procedures require the use of long-range strain gauges or extensometer to determine the strain. A chemical analysis was conducted to verify the specification by the manufacturer. The specimen was found to be fairly homogeneous with minor sulphide inclusions. The micrographs reveal a pearlite and ferrite structure typical of mild steel, and the fractographs show a dimpled surface typical of ductile fracture, which is an attribute of mild steel.

Jan 1, 2013

This paper describes experimental investigations into the reductive decomposition of arsenopyrite/pyrite (FeAsS/FeS2), a gold and silver bearing iron/arsenic sulphide using metallic iron powder. The main objective was to establish and experimentally confirm the thermodynamic and kinetic feasibility of reductively decomposing the sulphide matrix for precious metals recovery. In this context, cyanidation leach tests were conducted on the reductive leach residues. The arsenopyrite/pyrite flotation concentrate, mainly studied in the hydrochloric acid medium, decomposed through the non?oxidative chemical dissolution reaction and the reductive decomposition reaction for the arsenopyrite and pyrite components, respectively. Desulphurization levels below 65% were achieved at pH values below 0.15 and iron to concentrate ratios above 1, and the system was characterized by overall very slow kinetics. The reaction system had a direct linear relationship with iron to concentrate ratio and an inverse relationship with pH. An analysis of the pyrite/iron galvanic system showed that pyrite forms a partially inert cathodic surface on which the anodic dissolution of iron occurs, supported by the hydrogen evolution reaction. This phenomenon explained the low desulphurization levels and the mineral decomposition seemed to be restricted to the non?oxidative chemical dissolution reaction for the arsenopyrite component. The cyanide leach of the reductive leach residues showed very little improvement in gold recovery. The reductive leach process for arsenopyrite/pyrite has considerable limitations in terms of both desulphurization and precious metals liberation. Keywords: Pyrite, arsenopyrite reductive leaching, hydrogen sulphide, invisible gold

Jan 1, 2009