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By Kevin Stuffle, James E. Sharp, Sean Premeau

Two process enhancements for the biological oxidative pretreatment of sulfidic gold ore for subsequent treatment with cyanide are discussed. These are the use of a high areal density ring and pin packing (BioBalls™) as substrate, and the use of a novel biological ferric generator. The BioBall™ packing when coated with concentrates for heap leach processing offers higher areal densities, while leaving more open volume for fluid flow than more commonly used substrates such as aggregate. An oxidation rate study was performed on crushed auriferous arsenopyrite whole ore to demonstrate the benefits of using the packing. The auriferous arsenopyrite grading 2.9% Fe and .212 OPT gold was 50 percent oxidized in 24 days. The biological ferric generator is a passive air-side trickle bed reactor that efficiently converts ferrous to ferric in a process stream. Conversion rates of .8g/L h ferrous to ferric are routinely obtained. Although the biologically generated ferric solutions have not yet been tested on gold ores or concentrates, prior work has demonstrated that the high ferric solutions which will result in rapid oxidation of sulfidic gold ores or concentrates.

Jan 1, 1997

By John Keay, Douglas R. Shaw, Gregory J. Olso

Rhodes Mining NL, Perth, Australia, is developing the Lahoca Gold Project which is located in Hungary, about 30 km from the town of Eger. The preliminary resource is estimated to contain approximately 1.5 million ounces of gold. The project is being evaluated for an annual process capacity of 2 million tonnes. The test samples contain just over 2 g Ault and 6% sulfur as sulfide. Copper and arsenic levels are approximately 0.2 and 0.1 %, respectively. The ore is refractory due to submicroscopic gold occurrences and structural associations with pyrite. A small amount of the gold is finely encapsulated in quartz. Approximately 30% of the gold in the crushed ore is soluble in cyanide and up to about 55% is cyanide-recoverable with ultra­fine grinding. The ore has little preg-robbing ability. Metallurgical test work done by Colorado Minerals Research Institute (CMRI) and other investigators has shown that as much as 85 to over 90% of the gold was recovered by the relatively severe conditions of pressure oxidation or roasting of the whole ore or a flotation concentrate. The Lahoca ore responds to flotation with gold recoveries of 87% into a low grade concentrate. Subsequently, with a view toward defining a process route with potentially more attractive economics, Rhodes Mining and CMRI conducted an extensive review of biooxidation technologies and concluded that, in particular, heap biooxidation methods promised lower process costs which normally are associated with heap leaching. Based on the study, which included the analysis of the closely related practices of copper dump/heap bioleaching now well established in that industry, CMRI conducted simulated heap biooxidation experiments which evaluated factors such as ultra fine ore crushing, agglomeration techniques, heap design, forced aeration oxygen supply, and whether or not the heap is irrigated. Separate flask biooxidation tests at Little Bear Laboratories showed that the finely crushed ore is biooxidized readily, with a near linear relationship between sulfide oxidation and gold cyanide solubility. Gold recoveries of as high as 66% have resulted after biooxidation of crushed ore. This paper highlights the metallurgical developments of the Lahoca project, and focuses on recent biooxidation laboratory test work aimed at enhancing the treatment of crushed ore.

Jan 1, 1997

By Allen H. Gipson

Innovative thinking has led to the development of safe, environmentally sound, and cost effective methods for expanding existing tailings storage facilities (TSF). Three case histories are discussed here to demonstrate methods that have recently been used or are being considered for such expansions. Maintaining the integrity of the structure and reducing costs were primary goals in each case.

Jan 1, 1997

By Michael Botz, Craig McKenzie

Recovery of cyanide from mill tailings can be conducted to lower the overall cost of precious metals extraction, while lowering cyanide concentrations in mill discharges and potentially eliminating the need to chemically destroy cyanide. Recent applications of cyanide recovery based on acidification­volatilization-reneutralization (A VR) technology have elimi­nated the need for cyanide destruction and substantially increased the profitability at several gold and silver operations. Recent developments in the technology permits processing of scale-prone and high percent solids pulps while generally affecting cyanide recoveries in excess of 70% to 90%.

Jan 1, 1997

By Jeffery S. Thompson, Harry Hinds

Recent advances in the development and application of the DuPont Activator Technology are discussed. Activators are catalysts of gold dissolution in cyanide solution. Plant testing of this technology in the vat leach circuit of the Homestake mine in Lead, South Dakota, showed increased gold recoveries ofup to 5%. Homestake has licensed the technology for this application and is in the process of full commercialization. Results from testing additional ores on a laboratory scale are also presented. These results indicate this technology will also increase leaching at much lower cyanide concentrations while achieving the same gold recovery.

Jan 1, 1997

By V. Fred Swanson, J. Patrick Glynn

The environment for process engineers today is very different from 20 years ago. The ideas and mathematical description of models for a multitude of different unit operations is an ongoing development. The computer tools to deal with the mathematics are readily available and specialist companies have developed, tested and verified their models. The challenge for the process engineer is to know which package to use and to know whether a particular application is the most accurate for the specific process. Metallurgical simulation programs today are well known and proven. Certain programs are specialized while others are broader based. The needs of each user are dependent on the application. Typically, most users require the following operations: • Comminution • Flotation • Hydrometallurgy • Pyrometallurgy • Additional requirements could be defined as: • Thermodynamic capabilities for solids, phases, and gases • Dynamic simulation • Data analysis tools • Coal oriented operations • Diamond oriented operations

Jan 1, 1997

By R. H. Lien, B. T. Waterman

Passive bioremediation can be a cost effective treatment for a variety of mine waters, including final draindown of closed cyanide heap leaches and seepage from tails dams. These solutions can contain noncompliance concentrations of arsenic, antimony, cyanide, mercury, nitrate, selenium, silver, etc. Passive bioremediation involves treating the contaminated solutions under anaerobic conditions. Contaminants such as mercury and nitrate are effectively removed in passive bioreactors whereas the effect of this treatment on TDS, cyanide, and sulfate is minimal. Several waters from gold heap leach operations were treated in the column tests. These tests determined the effectiveness of contaminant removal from each water and also provided important scaleup design information.

Jan 1, 1997

By Chuck Hornaday, Brad Miller

Geosynthetic clay liners (GCLs) are manufactured barrier layers containing a high-quality sodium bentonite clay attached or adhered to geotextiles or a geomembrane. The GCL's low permeability and high strength make it an ideal replacement for low permeability soil or clay liners for mineral extraction and processing containment applications. This paper will discuss the advantages of utilizing a GCL versus compacted clay in containment applications. Some of the advantages include: the GCL's lower permeability (5 x 10-9 centimeters per second (cm/sec)) and corresponding better composite liner leakage protection, the GCL' s greater resistance to desiccation, differential subsidence and freeze­thaw, and lastly, the ease and speed of installing the GCL. This paper will also detail a number of important case studies related to the mineral extraction and processing industry. These case studies include using GCL in two large reclamation capping projects, as a secondary liner in two gold heap leach pads, as a composite liner in a dam for stormwater runoff control, and lastly, as a primary liner for a tailings runoff diversion channel.

Jan 1, 1997

By Leonard Harris

Since the end of the cold war following the collapse of communism, enormous amount of funds are pouring into the developing countries including investments by mining companies for the development of gold and silver mines. A great deal of these funds are destined for expenditure in areas riddled with bandits, terrorists and active and latent criminals bent on stealing the mine operators hard earned production on its way from the mines to markets. Brambles Security Services employs experts in the field of safely transporting gold and silver products under various alternatives and aimed at relieving the mine owners of this responsibility. This paper examines the various service options available.

Jan 1, 1997

By Harry M. Castrantas

Caro's acid (peroxymonosulfuric acid-H2SO5) is used to destroy cyanides in tailings slurries due to its rapid reaction and low capital and operating costs. Due to its instability, Caro's acid is generated at the mine site using a hot or cold process. The majority of gold mines that use Caro's acid use the FMC hot process. In the FMC hot process, it is not necessary to cool the Caro's acid to minimize decomposition since it is used immediately upon generation. In contrast, the cold process uses a chiller to cool the raw materials and product. This paper will show, using laboratory and field data, that there is virtually no difference in Caro's acid yield between the cold and the FMC hot processes. Caro's acid yield depends on the mole ratio and concentration of sulfuric acid and hydrogen peroxide and is independent of operating temperature.

Jan 1, 1997

By Robert Dunne, John Angove

The physical properties of an ore body require determination for virtually all mining projects, new and existing. The extent and regularity of such determinations being subject to the size and homogeneity of the orebody. Such properties have an impact at the design stage of new plants, with respect to equipment specification, and thus effects capital costs; and also impacts on the operating costs of new and existing plants, with respect to power consumption, production levels and part replacements. All of these can severely alter the bottom line and can be the determining factor in the economic viability of many projects. This paper examines some of the most common properties that are measured, the procedures utilised in determining these properties, and their variability under conditions of reproducibil­ity, and to a lesser extent repeatability. The properties looked at were Impact Crushing Work Index, Abrasion Index, Bond Rod Mill Work Index and Bond Ball Mill Work Index. A number of testing laboratories throughout Australia and the US were utilised in the survey. The results showed up some interesting and important features of the procedures used, all of which have become accepted industry standards, and which had varying effects on the final result. Tests such as the rod and ball mill indices would appear to have reasonably robust procedures which allowed for the determinations of the respective index without the introduction of significant variations, although there were indications that variations could occur. The other tests gave a sufficiently different picture to be able to suggest that an argument could be made for a more intensive investigation to be undertaken, with the possible outcome that a modified test procedure or an alternative test is required.

Jan 1, 1997

By Gary L. Simmons

Many large (refractory) sulfide gold resources exist in Nevada and other parts of the world that are not amenable to conventional flotation concentration using air as the flotation gas medium. Over the past five years Santa Fe Pacific Gold Corporation (SFPG) has investigated flotation process options to economically treat refractory ores and resources of this type at its Lone Tree and Twin Creeks mines. Conventional flotation technology applied to the original high-grade gold resources at Lone Tree and Twin Creeks was initially unsuccessful. Review and analysis of auriferous (gold-bearing) iron sulfide mineralogical characteristics and flotation ..:hemistry provided a fundamental understanding that led to the development of a new flotation process that SFPG refers to as N2 TEC. This paper discusses the development of this technology and compares N TEC results with conventional flotation practice.

Jan 1, 1997

By Terry I. Mudder, Michael M. Botz

Discharge regulations for mine waters require relatively low concentrations for cyanide and metals, and the trend is for discharge limits to be lowered. In the event conventional treatment practices are not sufficient to meet discharge limitations, advanced treatment technologies such as ion exchange and reverse osmosis may be considered. Though these technologies will provide discharge quality waters, they also require the disposal of a concentrated brine and are relatively complex and costly to operate. Many mine sites currently using activated carbon in precious metals recovery present the opportunity to economically operate an activated carbon water treatment plant for polishing of effluents. This paper presents summaries of six ( 6) mining operations which have evaluated or use activated carbon for treatment of water and which also use carbon in precious metals recovery processes.

Jan 1, 1997

By Andreas Rubo, Stephen Gos

In the days of increasing environmental and safety awareness many efforts have been made to prevent losses of both an evident economic nature and also less obvious losses. These losses could be associated with damages due to negative impact on the environment and also people coming into contact in a broader sense with any toxic chemical. This paper deals with how cyanide can be applied in a responsible manner at a modern gold mine. Responsible application is achieved by minimizing losses of reagent and avoiding negative impact on the environment as well as adopting a Responsible Care philosophy to the application of cyanide. It becomes evident that this is quite a complex system with a greater commitment than avoiding reagent losses for economic purposes.

Jan 1, 1997

By P. Riveros, J. Binvignat, V. M. McNamara, D. Koren

The feasibility of recovering cyanide and copper from a gold mill barren solution was evaluated in a small A VR pilot plant. The campaign lasted 64 hours, during which time about 4,000 L of gold mill barren solution were processed. The results showed that A VR is an effective technology for recovering cyanide and copper from barren solutions. Under the best conditions, the copper precipitation and the cyanide volatilization attained 94% and 98%, respectively. Using 5 MNaOH as the absorbent, practically all the HCN gas was recovered in the form of a concentrated NaCN solution containing 70 g/L free CN. Basic engineering design parameters applicable to a large-scale operation were obtained, including the Henry's Law constant and the mass transfer coefficient for HCN gas.

Jan 1, 1997

By F. P. van der Meer

Roller Press grinding has become an accepted technology in the cement industry, and finds a growing application in iron ore processing. Its introduction to the gold industry will depend on anticipated benefits such as a reduction in power requirements, the increase in throughput, and higher gold recoveries from the ground ore. The presentation highlights some of the specific features of the KHD Humboldt Wedag Roller Press and the effects of various operating parameters on the grinding result. Based on recent experiences examples are given on the use of the Roller Press in mineral applications. The anticipated reduction of grinding energy when using the Roller Press is discussed, together with the reduction in Bond Work Index.

Jan 1, 1997

By Andrew P. W. Briggs, Corale L. Brierley

A considerable economic and technical knowledge base has been amassed with the successful and sustained operation of commercial minerals bioleaching/biooxidation plants to extract copper from chalcocite ore and enhance precious metal recovery from sulfidic refractory ores and concentrates. Economic evaluation ofbio-processing must consider the value of the ore, the sulfide-sulfur requiring oxidation to achieve significant metal recovery, the time required for the biological process and, in the case of precious metal feed-stocks, the down-stream reagent consumption. Of these considerations oxygen requirement for the biologically-catalyzed oxidation of sulfide minerals is the prevailing determinant in the capital and operating costs of aerated, stirred-tank reactors for processing concentrates and bio-heaps for processing ores. Oxygen requirement is dictated by the amount of sulfide-sulfur requiring oxidation to achieve desired metal recovery. The testwork program to evaluate a project for application of biooxidation/bioleaching must be designed to insure that factors critical to economic assessment are fully quantified.

Jan 1, 1997

By Ethan B. Eilertsen

Titanium solves corrosion, maintenance and environmental problems in many reactor and autoclave applications. Titanium clad construction permits autoclave designers a great deal of flexibility combined with significant cost reduction. Titanium alloys can be selectively applied in specific regions of the autoclave to accommodate local environmental conditions. Resistance to general corrosion, crevice corrosion, abrasion, and ignition conditions can be accomplished selectively and economically. Explosion clad pressure vessel fabrication and performance have been proven through three decades of experience.

Jan 1, 1997

By B. A. Firth

The presence of misplaced ultra-fine particles has been shown to decrease the separation efficiency of unit operations used in coal preparation. Although the classification of fine coal was considered to be adequate for the needs of the coal industry during the 1970's and 1980's, it has become apparent that further improvements in the yield/ash/moisture relationship achieved by coal preparation plants will require increased efficiency in this size separation step. This paper describes the issues which are evolving in this area, and the capability of current and developing techniques to address the problems which need to be overcome.

Jan 1, 1996

Current scrubber capacities vary from 1.89 to 4.72 m3/s (4,000 to 10,000 cfm), and there is interest in using scrubbers with capacities up to 6.61 m3/s (14,000 cfm). This paper describes research to compare the effectiveness of blowing and exhausting face ventilation systems using high-capacity scrubbers with flows up to 6.61 m3/s. Tests were conducted in a surface ventilation gallery with exhaust and blowing systems operating under similar conditions. The mining machine was equipped with a machine-mounted scrubber. Methane gas was released at constant flow at the mining face and measured at several face locations. Effectiveness of exhausting and blowing systems was compared by determining average face methane concentrations. For each operating condition tested, blowing ventilation was more effective than exhausting for controlling face methane levels. Raising scrubber flow to 6.61 m3/s reduced methane levels for both blowing and exhausting systems.

Jan 1, 1996