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By K. A. Lewandowski

The efficiency of heap leaching is reduced by poor solution flow characteristics (i.e., channeling and ponding) that result from fines migration. Agglomeration of the ore can immobilize fines, but for agglomeration to be successful in copper leaching, an acid-resistant binder is needed to stabilize the agglomerates. Until now, there has not been a satisfactory method to evaluate whether a binder was effective, other than squeezing a handful to see if it ?feels right.? This paper reports on several procedures that have been developed to quantitatively determine whether a binder gives good performance in an acidic solution. These procedures have been used to identify binders that would be suitable for copper heap leaching.

Jan 1, 2008

By Terry D. Vandell

The purposes of this presentation are: (1) to discuss the actual as well as potential incidents that have caused and that could cause groundwater contamination at uranium in situ leach mining sites and (2) to discuss remedial actions and solutions that have been or that could be implemented in the future to stop or prevent serious groundwater contamination from in situ leach mining in Wyoming?s Powder River Basin. Open pit, underground, and existing and proposed in situ leach uranium mine sites in the Powder River Basin are shown in Figure 1. In situ leach mining or solution mining for extracting minerals in liquid form is a relatively new addition to the list of conventional mining methods currently used to extract uranium in Wyoming's Powder River Basin. Basically, the in situ leach mining method involves: (1) the injection of a leach solution lixiviant (an acidic or basic oxidizing solution) into a uranium-bearing ore body, via injection wells, to complex the contained uranium, (2) mobilization of the uranium complex from the host material via creation of a soluble complex salt, and (3) surface recovery of the solution bearing the uranium complex via production wells. Uranium is then separated from the leach solution by conventional milling unit operations (ion exchange).

Jan 1, 1981

By C. Athanassopoulos

Geomembranes have been used in the mining industry since the early 1970s in solution and evaporation ponds, tailings impoundments, and heap leach pads. Traditionally, heap leach pad lining systems have consisted of a single geomembrane liner placed directly over a prepared subgrade of locally available soil. Heap fills are constructed by placing a layer of highly-permeable drainage stone (overliner) over the geomembrane. Crushed ore is then placed on the leach pad in 3- to 10-m (15- to 30-foot) thick lifts, sometimes reaching final heights of several hundred feet. The crushed ore is irrigated with a chemical solution which dissolves the precious metals from the ore. The nature of the chemical leaching solution depends on the metal being targeted. Low pH sulfuric acid solutions are generally used to leach copper and nickel; high pH cyanide solutions are used to leach gold and silver. The metal-laden pregnant leach solution (PLS) passes down through the ore pile and is captured in a drainage system. Metals are extracted from the leach solution and the solution is then recycled back onto the leach pile. When under load, geomembranes are vulnerable to damage from large stones both in the soil subgrade and in the overlying drainage layer. Although intact geomembranes are virtually impermeable, installed geomembranes will have a small number of holes due to imperfect seams or damage during construction and filling operations. These holes serve as open pathways for leakage into the soil below. Smith and Welkner (1995) estimated liner leakage rates ranging from 5 to 10,000 L/ha/day, depending on the type of heap pad liner and level of construction quality assurance (CQA). Thiel and Smith (2003) reported liner leakage rates up to 2,000 L/ha/day for a valley fill facility with heads ranging from 15 to 35 m.

Jan 1, 2011

By N. L. Hayward, V. H. Ness

In the past decade Australia has seen the development, construction and commissioning of three complex processing plants for the treatment of lateritic nickel ores. These have all been based on high pressure acid leaching (HPAL) for extraction of nickel and cobalt into solution, followed by solid liquid separation in a CCD circuit. However, flowsheets for separation and purification of the nickel and cobalt diverge markedly. The existing plants have been commissioned with varying degrees of success, with a variety of problems ranging from materials of construction to inadequate design. While the process problems are not insurmountable, there is much room for improvement. Currently there are several new HPAL plants at the feasibility or financing stage. All of these have adopted one of the existing flowsheets. Most of the enhancements have focused on increasing autoclave size. It is now time to assess the success and failures of the three existing plants and incorporate this experience in a design for productivity, efficiency and reliability. Towards this end, this paper discusses aspects of flowsheet optimization, materials of construction and engineering design.

Jan 1, 2001

By H. K. Lin

The free-milling ore characteristics of the Fort Knox gold deposit are ideal for studying gold and silver behaviors in various processing circuits without serious interference of sulfide minerals and other refractory factors. A galvanic effect leads to faster silver dissolution than gold dissolution and, as a result, the Au/Ag solution concentration ratio increases through the leach circuit. In the CIP circuit, Au adsorption is more effective than Ag adsorption. The Au/Ag solution concentration ratio decreases from 10.0 to 1.0 as the slurry advances from CIP tank #1 to CIP tank #5, while Au/Ag ratio in the carbon increases from 3.2 to 15.3, as the carbon advances from CIP tank #5 to CIP tank #1. Silver is stripped more effectively than gold from the loaded carbon. The Au/Ag ratio in solution reaches 2.0 in the first 75,700 L of strip solution that pass through the loaded carbon; as the stripping process continues, the Au/Ag ratio in the strip solution increases. In the electrowinning circuit, the Au/Ag ratio in the spent electrowinning solution is significantly lower than that in the electrowinning feed, indicating that Au is more rapidly deposited onto the cathode than Ag.

Jan 1, 2010

By S. Painter

The effects of forced ventilation and thermal radiation in open drifts are included in three-dimensional thermal hydrology simulations of a potential waste repository at Yucca Mountain, Nevada. A semi-analytical model is used to calculate the amount of waste heat removed by ventilation air during each time step of the multiphase thermal-hydrology simulator. The model accounts for thermal radiation and changes in air temperature and humidity along the emplacement drifts. The fraction of heat removed by ventilation is time and position dependent.

Jan 1, 2004

By J. Olsson

Introduction Stainless steel has by tradition been a common construction material for hydrometallurgy processes and the most common grades can be found amongst the ASTM 300-series, i.e. austenitic grades of type 304L, 316L and 317L. However, there are a number of new grades available today, which imply more cost effective solutions for those designing plants where good resistance to acids, containing the desired metal ions, often contaminated with chlorides and other halides, is the key issue. There are austenitic-ferritic or duplex grades having the same or even better corrosion resistance than the austenitic grades and approximately twice the strength, which enables design in thinner gauges, which in turn implies less weight and less cost. They have also excellent engineering properties, enabling fabrication of process equipment, machinery and different types of tanks. On top of that, they contain less nickel and molybdenum than their austenitic counterparts, which implies not only lower cost for alloying elements, but also a more stable price when considering the price fluctuations for these alloying elements during the last years. This paper describes briefly the family of duplex stainless steel and it presents a number of relevant corrosion tests where duplex grades have been compared with austenitic grades. The results have in several cases been verified by in-plant exposures in zinc and copper production plants. It also describes applications and experience of duplex grades within a variety of hydrometallurgy plants. Installations of highly alloyed austenitic grades will be described as well. The corrosion tests and service experience reported cover hydrometallurgical processes based on sulphuric acid.

Jan 1, 2007

Water conservation and compliance strategy can be cause for success or failure of a new or existing mining operation. Water accounting at outset, and pit and waste dump planning, may not fully consider total inflows, or sediment loads encountered during mine life. Environmental impact assessments, and permitting often dictates the rules, and these may change, to be more stringent, during course of mine development. This paper will identify techniques to control unprojected fresh water, or increased surface water flows in surface mine operations.

Feb 23, 2014

By N. B. Aughenbaugh

The People's Republic of China has 582 Gt (641 billion tons) of proven coal reserves. At present, 576.5 Mt (635.5 million tons) of coal are mined a year which makes China the third largest producer of coal in the world. Underground mining accounts for 95% of the total production. This paper will discuss the coal districts, coal types, jurisdiction of coal mining, and methods of underground mining. The article also will outline China's objectives in future planning and development of its coal reserves.

Jan 1, 1982

By Ken Deter

My recent experience has been with wet tropical environments, which address a different set of concerns than Nevada, for example. Spraying rather than drips are required in most cases just to assist the water balance requirement, and my comments address those situations. Most tropical operations are faced with both extremely wet and very dry seasons, with some having multiple cycles during the year. A heap leach operation must address the rate of solution building up within the ponds and how long the volume must last until the next rainy season. It may be easier to construct sufficient pond volume to permit yearlong operation than by discharging excess solution now, and searching for water later. Pond capacity requirements can help with the following: Consider using the solution that could be locked up in the pads during leaching to assist water balance problems. Spray excess solution continuously onto spent ore that would not be normally be sprayed again to "soak up" the excess solution, and stop spraying when the water balance is low, allowing the solution in the spent ore to return back into the system-with or without cyanide added. In a multiple lift system, if intermediate HDPE liners are planned for solution grade control, have drips placed before the HPDE liner is in place. The drips can distribute excess precipitation throughout the lower lifts to control the water balance, while the most current lifts are being leached and sent directly for the preg pond. With only 2 million tonnes (2.2 million tons) of spent ore involved, up to 200,000 cubic meters (53 million gallons) of solution could be moved into or out of the water balance system, if proper methods are designed and installed. That is equivalent to one meter (40 inches) precipitation falling on a 200,000 square meter (2.2 million square feet) pad area. You may even get a little bit more gold recovered as the solution drains from the earlier pads, as well.

Jan 1, 1999

Previous models describing the aggregation of polymer coated particles fail to take into account the fact that there are a limited number of sites onto which a polymer segment can adsorb, called ?active? sites. Thus, the collision efficiency is a factor not only of the fractional surface coverage, but also of the number of active sites. In this study, a physical model of the flocculation system was devised in which the number of these sites could be varied, in order to study the effect on particle aggregation.

Jan 1, 1987

By D. A. Stanley

The Bureau of Mines has developed an equation which describes the dewatering of clay slurries with polyethylene oxide. This dewatering equation is An _ kC + b where n, k. and b are empirical constants and C is the concentration of polymer solution used for dewatering. The minimum amount of polymer required for dewatering. A is determined by titration of the clay slurry with a polymer solution. In this report, the dewatering equation is applied to data obtained for a polyacrylamide dewatering sequence. Fundamental similarities between the dewatering properties of clays and the viscosity of polymer solutions were observed. These similarities were explained by correlating an equation describing polymer configuration in solution with the dewatering equation. This correlation showed that amount of polymer required for dewatering and polymer solution viscosity are both consequences of the frictional interaction of entangled polymer coils.

Jan 1, 1989

By Allan J. Breitenbach

Heap leach operations provide a low-cost method for recovering gold, silver, and copper metals from low grade ore materials. The processed ore materials are stacked in controlled lifts on a lined pad facility for heap leaching. A controlled barren solution is applied to the heap ore surface by sprinkler or drip emitter irrigation, and ore metals are leached into the solution for collection and extraction in plant process facilities. The leach pad and solution collection facilities are lined with impervious materials for containment of all process solutions. The liner system typically includes a composite geomembrane and clayey soil liner with a protective drain cover fill to maximize solution recovery and protect the underlying groundwater conditions. This paper discusses the types of pad liner systems currently used by the mining industry and the "good, bad, and ugly" lessons learned in engineering practice over the last 10 years in the design and construction of heap leach pads.

Jan 1, 1999

By B. J. Scheiner, D. A. Stanly, P. M. Brown

The Bureau of Mines has developed an equation that describes the dewatering of clay slurries with poly- ethylene oxide. This dewatering equation is: A[ ] = KC + b where n, k, and h are empirical constants and C is the concentration of polymer solution used for dewatering. The minimum amount of polymer required for dewatering, A, is determined by titration of the clay slurry with a polymer solution. In this report, the dewatering equation is applied to data obtained for a polyacrylamide dewatering sequence. Fundamental similarities between the dewatering properties of clays and the viscosity of polymer solutions were observed. These similarities were explained by correlating an equation describing polymer configuration in solution with the dewatering equation. This correlation showed that the amount of polymer required for dewatering and polymer solution viscosity are both the consequences of the frictional interaction of entangled polymer coils.

Jan 1, 1991

By Chunlin He, Xinsheng Li, Feng Yang, Lu Han, Yuezhou Wei, Feng Gao

The solvent extraction of vanadium (V) from Na2CO3–NaHCO3 solution was attempted using Aliquat-336 (methyltrioctylammonium chloride) extractant dissolved in sulfonated kerosene as diluent with 2-octanol as phase modifier. The influence factors, such as Na2CO3 concentration, NaHCO3 concentration, temperature, extractant concentration and impurity P, on vanadiumextraction were investigated. The results revealed that the single stage extraction efficiency of vanadium reached above 89%from 20 g/L Na2CO3 – 20 g/L NaHCO3 solution under the following conditions: extractant concentration of 15%, room temperature of 20–30 °C, 2-octanol of 6%, phase ratio (O/A) of 1:1, and oscillation time of 1 min. The addition of NaHCO3 into Na2CO3 solution could lower the pH value of the Na2CO3 solution, improve extraction efficiency of vanadium, and not introduce other impurities. The phosphate anion did not interact with the vanadate anion in the Na2CO3–NaHCO3 solution. The P in the Na2CO3–NaHCO3 solution had little influence on vanadium extraction.

Jul 30, 2020

By A. McCombs

Previous models describing the aggregation of polymer-coated particles fail to take into account the fact that there are a limited number of sites onto which a polymer segment can adsorb, called "active" sites. Thus, the collision efficiency is a factor not only of the fractional surface coverage, but also of the number of active sites. In this study, a physical model of the flocculation system was devised in which the number of these sites could be varied, in order to study the effect on particle aggregation.

Jan 1, 1988

By Gill G. Geesey, Michael R. Hankins, Paul L. Wichlacz, Anita Gianotto, John G. Jolley, Randy B. Wright

Thin films of copper [2.0 nm on germanium internal reflection elements (IREs) and 3.4 nm on germanium discs] were exposed to 10% gum arabic (aqueous solution) , 2% alginic acid (aqueous solution), 1% bacterial culture supernatant (BCS, simulated seawater solution) and 0.5% Pseudomonas atlantica exopolymer (simulated seawater solution). The IRES were monitored in situ, in real time using fourier transform infrared/cylindrical internal reflection/attenuated total reflection spectroscopy as a function of time at ambient conditions. The discs were characterized (pre- and post-exposure) by X-ray photoelectron and Auger electron spectroscopies. Ancillary graphite furnace atomic absorption spectroscopy was used to monitor the removal process of the copper thin film from the germanium substrates. Results indicate that Cu was oxidized by gum arabic, alginic acid and BCS. Furthermore, Cu was removed from the Cu/Ge interface by all four polymers. The Cu was found associated with the polymer solutions.

Jan 1, 1989

By John A. Lombardi

The solutions used in the heap biooxidative treatment of sulfidic refractory Au ores and concentrates generally load free mineral acid and metals and, in time, become bacteria activity inhibiting due to increased acid and/or metals concentrations. The metals­acid loaded, bacteria action inhibiting, solution must then be: (a) processed, prior to re-use, to reduce its metals and/or free acid mineral acid components to bacteria activity compatible levels; or (b) neutralized prior to discharge. The most common solution processing method to adjust acid-metals contents is liming to effect the precipitation of dissolved metals and neutralization of acid sufficient for solution discharge or re-use. The lime treated solution is high in suspended, colloidal precipitates and requires clarification before reuse. Most often the "bleedstream" of biooxidation solution that is lime treated is discharged and req­uisite volumes of fresh water added to the process inventory. Depending on the level of bacterial action in a heap and the acid consumption characteristics of the ore/concentrate being biooxi­dized, the bleedstream taken from the circulating, irrigation on­off, solution, can be large (e.g., 10%-20% and sometimes as much as 50% of the daily solution flow requires treatment-dis­charge). The lime charge for bleedstream treatment is commen­surately large and represents a major operating cost of the bioox­idation process. The patented HW Process Technologies (HWPT) Engineered Membrane Separation (EMS™) method is an alternative biooxi­dation bleedstream treatment method. EMS™ processing removes the multivalent base metals ions in an acid solution to a small volume EMS™ "concentrate" (typically 25% of the feed­stream volume). The EMS™ method coincidentally makes a "clean acid" EMS™ "permeate" (typically 75% of the feed­stream volume). In general, EMSTM processing enables 75% of the bleedstream volume to be recycled; allows up to 2/3 of the bleedstream acid to be recovered as a 10% solution; and delivers dissolved metals in a highly concentrated stream suited to a. metals recovery or b. reduced cost lime neutralization for a given metals precip­itation relative to full bleedstream neutralization (typically a 30% lime use savings). Implicit in the recovery of process water for re-use and reduced reagent addition requirement for metals precipitation is a significant reduction in wastewater-sludge dis­posal facility size.

Jan 1, 1998

By A. K. Stagg

Toxic substances in On solutions can retard biological leaching of copper sulfide dump ores. On solutions were analyzed for metals, organics, and chloride, and showed inhibitory concentrations of aluminum, manganese, and chloride. Inhibition of bacterial activity by the solid fraction of On solution, with and without the organic constituents, was evaluated. Toxicity to bacterial species was evaluated by monitoring bacterial numbers, pH, Eh, and rates of iron oxidation. The On solution solids were toxic at 50 -60% of their field concentration. Most of the toxicity of the On solution was due to the organic fraction. Different SX reagents show varying degrees of inhibition of T. ferrooxidans. Bacterial inhibitory effects of carriers and lixiviants used in the SX plant should be determined so that entrained SX reagents do not retard biological dump leach systems. The reagents used should be the most cost effective and the least toxic.

Jan 1, 1994

By L. A. Panek

A new pillar strength formula is presented, incorporating a function P of size and shape, which takes into account the size-shape interaction effect as well as the enhanced strength exhibited by wide pillars. Existing pillar formulas, lacking these capabilities, are not suitable for extrapolating small-specimen test results to mine-pillar sizes and shapes. Interpreting compressive-strength test results as function of P clearly reveals wide-pillar behavior in much old test data. Model relationships are discussed, along with their scaling implications.

Jan 1, 1994