About David

Since 1993, when he obtained his Mining Engineering Degree from Queen’s University, David has acquired experience in operating roles including many years in post-commissioning operations troubleshooting. Mineral Processing and Metallurgy has become a core strength and passion for Mr. Michaud. Learn more at

Rhenium Extraction by Leaching in Ammonium Iodide Iodine

leaching distributionPure rhenium is a refractory metal with a very high melting point of 3180°C.  Extraction of rhenium from molybdenite concentrates and other primary sources has been studied for many years. Hydrometallurgical methods using Br2, HNO3, Ca(OH)2, NaOH or Na2CO3 have been investigated. Recently, a new process using halogen salts and ammonium as well as oxygen for recovery of platinum group metals and rhenium was developed. This new process employs iodide/iodine and/or other halogen salts to effectively extract platinum group metals and rhenium from spent automobile exhaust catalysts and petroleum refining catalysts.

Usually rhenium used in catalysts is in metallic form. It disperses in catalyst matrix as very fine particles. Spent petroleum refining catalysts contain up to about 2500 ppm of rhenium together with a substantial amount of platinum. The new process using halogen salts is based on the fact that platinum group metals and rhenium metal are soluble in leaching solutions containing halogen salts and ammonia under appropriate conditions. However, the fundamentals of this new process are not fully understood.

The leaching behavior of gold and platinum in iodide/iodine solutions has been studied.

By | 2018-04-30T11:01:59+00:00 April 25th, 2018|Categories: Hydrometallurgy|Tags: |Comments Off on Rhenium Extraction by Leaching in Ammonium Iodide Iodine

Acid Leaching Copper Flotation Concentrate

As an alternative to Acid Leaching, Copper Chalcopyrite (CuFeS2) concentrates are processed traditionally by smelting, which results in sulfur dioxide (SO2) emissions. The development of a hydrometallurgical process for recovery of metals from concentrates of Cu ores offers industry a low-cost, low-pollution alternative to the traditional pyrometallurgical practices. The hydrometallurgical leaching of chalcopyrite with acid ferric sulfate solution as an alternative process to smelting has been studied extensively. The leaching process can be summarized by the chemical reaction shown below.

CuFeS2 + 4Fe+³ → Cu+² + 2S° + 5Fe+².

Munos, Miller, and Wadsworth have suggested that the principal rate-limiting step is the transport process of electrons through the dense, tenacious layer of elemental sulfur (S°) deposited by the reaction of chalcopyrite particles on the unreacted core. Figure 1 shows the S deposited on the surface of partially reacted chalcopyrite.

Several proposed processes for leaching chalcopyrite with ferric sulfate incorporate a grinding step to enhance the leaching kinetics. In the University of Utah-Martin Marietta process, concentrates preground to 1 m are dissolved by a two-step, 15-h leach at 90° C with an intermediate step to remove the S coating from the particles. The

By | 2018-04-25T07:56:31+00:00 April 22nd, 2018|Categories: Hydrometallurgy|Tags: |Comments Off on Acid Leaching Copper Flotation Concentrate

Large Melting Furnace – City Waste

The most widely applied method for the disposal of waste materials, including sludges, dusts, scales, leachable slags from smelting or melting operations, and residues from the combustion of organic materials including municipal wastes, is to inter the materials in an appropriate landfill. Small quantities of some wastes are encapsulated within Portland cement or sulfur, and then consigned to a landfill. However, landfill disposal of wastes is at best a short-term solution, because landfills are nearing capacity and new landfills are difficult to establish. A promising and technically viable permanent solution to the problem is to melt the waste materials to produce inherently non- polluting amorphous or crystalline mixtures of inorganic oxide products, similar to slags produced by various metal industries. These products may be useful as aggregate for bituminous or Portland cement concrete, for grit blasting, as road building and construction ballast, and in the manufacture of mineral wool instead of landfill disposal.

In 1984, the ASME Research Committee on Industrial and Municipal Waste asked the U.S. Bureau of Mines about the feasibility of melting (vitrifying) ash residues produced by the combustion of municipal wastes. A demonstration melting test of dry

By | 2018-04-22T03:23:55+00:00 April 21st, 2018|Categories: Smelting - Melting - Refining|Tags: |Comments Off on Large Melting Furnace – City Waste

How to Recover Metal from Mine Drainage Water

To recover metals as sulfide concentrates from contaminated waste streams using hydrogen sulfide (H2S) generated by the bacterial digestion of waste organic materials.

The goal of this research is to develop a treatment method for metal mine effluents that will rival the cost and convenience of conventional lime treatment, and that will provide better effluent water quality, result in less expensive sludge disposal, and allow for the selective recovery of metals.

How it works

In this method (fig. 1), indigenous sulfate-reducing bacteria are used to generate H2S gas in an anaerobic bioreactor containing sulfate-rich mine water and inexpensive, degradable organic matter such as food processing wastes or primary sewage sludge. As H2S is formed, it is sparged from the bioreactor by an inert carrier gas to create a gas stream containing about 0.3 pct H2S. When the gas comes in contact with a metal-contaminated mine effluent, the heavy metals precipitate as relatively insoluble sulfides. Elemental sulfur (S°) also may be formed. By adjusting the pH, the composition of the precipitated concentrates of metal sulfide can be manipulated. For example, the pH of mine water containing Cu, Zn, Fe, Al, and Mn

By | 2018-04-21T10:42:59+00:00 April 21st, 2018|Categories: Environment & Tailings, Recycling|Tags: |Comments Off on How to Recover Metal from Mine Drainage Water

Recover Neodymium from Permanent Scrap Magnet

Develop hydrometallurgical or pyrometallurgical recycling methods to recover valuable rare-earth compounds from various forms of NdFeB magnet scrap.

The U.S. Bureau of Mines (USBM) has developed technology to treat and recycle a variety of wastes containing valuable and strategic metals. As part of this effort, the USBM developed a process to separate neodymium and other valuable rare earths from iron in NdFeB magnet scrap (fig. 1). Since this scrap typically contains nearly 30 weight percent neodymium and since the demand for neodymium is constantly increasing, cost-effective methods for scrap treatment could have a significant impact on industrial expenditure and materials supply in the expanding area of magnet manufacture.


A hydrometallurpical, H2SO4 dissolution-precipitation process provided the most effective treatment for separating rare earths from bulk NdFeB magnet scrap (fig. 2). Precipitation of neodymium-alkali sulfate double salt proved advantageous over direct precipitation of fluoride or oxalate products. This double salt is easily converted to a variety of useful rare-earth compounds, which eliminates, many of the materials handling and economic problems inherent with direct precipitation. Following rare-earth precipitation, dissolved iron was removed from the acid leach solution by precipitation as a jarosite.

By | 2018-04-30T11:02:24+00:00 April 21st, 2018|Categories: Recycling|Tags: |Comments Off on Recover Neodymium from Permanent Scrap Magnet

How to Make Graphite Flakes from Steel Waste

Develop a technology for producing high-quality flake graphite from the steelmaking waste known as kish.

Approach: Treat the waste kish as an ore and apply mineral processing techniques of physical beneficiation and chemical purification to produce a range of graphite products competitive with the natural mineral.

Graphite is a naturally occurring form of carbon with a unique combination of properties that make it indispensable in a very wide range of industrial and consumer applications. It has high electrical and thermal conductivity and remains stable to extremely high temperature. It has a low coefficient of friction and is nearly impervious to corrosion. The steel industry is dependent on graphite in clay-, magnesia-, and alumina-bonded refractories for crucibles, bricks, facings, and coalings. Electrical uses include graphite brushes in motors and generators, and electrodes in batteries. The transportation industry needs graphite for clutch and brake linings, and all industries depend on graphite in seals, gaskets, lubricants, and coatings. The consumer sees (graphite in composite plastics and in the common pencil.

As with all natural minerals, the availability of graphite is diminishing and costs are rising as quality decreases.

Furthermore, the United States is totally dependent mi

By | 2018-04-21T10:43:37+00:00 April 21st, 2018|Categories: Recycling|Tags: |Comments Off on How to Make Graphite Flakes from Steel Waste

Ball Mill Scale-up Method

Ball Mill Scale-up by this method is known as collision energy based population balance model. The appropriateness of this model is shown for 38-cm ball mill. Comminution in ball mills account for a significant amount of power consumption in mineral processing plants. Therefore, accurate modeling of the process is extremely important to optimize the power consumption, which can lead to substantial economic benefit. In the past few decades, a plethora of research work has been published that dealt with ball mill scale-up. The first systematic scale-up procedure was proposed by Bond. By means of a set of grinding experiments conducted in a laboratory mill a parameter known as “Bond’s work index” is determined. This parameter is an indicator of the material strength subject to the mill operating conditions. Material work index is then scaled up for larger size mill and correlated with mill power, mill dimensions and operating conditions. In the later stage all the scale-up methodologies were formulated on the basis of the population balance model, also known as selection/breakage function model. All these methods suggest a way to determine the selection and breakage function suitable for modeling the

By | 2018-04-16T12:31:21+00:00 April 16th, 2018|Categories: Grinding|Tags: |Comments Off on Ball Mill Scale-up Method

Copper Activation Sphalerite & Xanthate

Copper Activation Sphalerite & Xanthate: Unlike most other sulfide minerals, sphalerite responds poorly to short-chain thiol collectors. The problem is attributed to the high solubility of zinc-thiol compounds in water. Also, due to its large band gap (3.7 eV), sphalerite is a poor catalyst for mixed potential reactions between xanthate and oxygen.

The reactivity of sphalerite with xanthate improves when the mineral is activated by heavy metal ions, such as copper, to form a copper sulfide, as follows:

ZnS + Cu²+ → CuS + Zn²+……………………………………………………….(1)

which in turn reacts with the collector to form stable copper xanthate to render the mineral surface hydrophobic.

It is well known that sphalerite flotation is sensitive to pH. Kartio, conducted XPS studies on copper-activated sphalerite in alkaline pH. The results showed that a CuS-like activation product is formed in deoxygenated solutions, while copper polysulfide is formed in air-saturated solutions. This finding provides an explanation for the collectorless flotation of copper-activated sphalerite. Other investigators identified elemental sulfur, rather than the polysulfide, as the hydrophobic species when sphalerite was copper-activated in acidic solutions.

It is well known that sphalerite flotation is difficult in the neutral pH range. Sutherland attributed the

By | 2018-04-18T19:15:57+00:00 April 16th, 2018|Categories: Flotation, Reagents & Chemicals|Tags: |Comments Off on Copper Activation Sphalerite & Xanthate

Recover Gold with Liquid Carbon Dioxide

We propose a liquid-liquid separation of free or liberated gold from gangue and metallic minerals. This technique involves contacting an aqueous slurry of hydrophobic and hydrophilic particles with a non-aqueous phase. The favorable surface interactions between the non-aqueous phase (typically oil) and fine hydrophobic particles cause them to be either dispersed within the non-aqueous phase or to agglomerate at the water-oil interface. recovery of gold high pressure contact angle apparatus

Experimental Procedures


Carbon dioxide (99.9%), which was maintained at or above its vapor pressure to occur in the liquid phase, was used as the non-aqueous phase in most experiments. Hexane was also employed as a non-aqueous phase. Dodecanethiol was used in several experiments in an attempt to enhance the hydrophobicity of the gold surfaces.


Pure gold, platinum and silver disks (David Fell) were used in the surface study experiments. These surfaces were first used as received and subsequently polished with 1-micron diamond paste to a proof-like finish. An unprotected gold mirror and a quartz optical flat were also used. One of the triangular surfaces of a large octahedral magnetite crystal from the Central African Republic

By | 2018-04-16T11:06:51+00:00 April 16th, 2018|Categories: Precious Metals|Tags: |Comments Off on Recover Gold with Liquid Carbon Dioxide

Ferrosilicon Powder

Ferrosilicon powder (containing approx. 15% Si) for constitution of heavy media is used today in many separation plants treating iron and other ores. The production of the powder by grinding is expensive. A new process atomizes the still molten ferrosilicon by air or steam.

In a heavy medium this atomized ferrosilicon powder has several remarkable properties: The round form and smooth and shining surface of the individual grain offers greater resistance to corrosion, especially as no contamination is produced between iron and silicon during the process. The viscosity of the heavy media pulp for the same weight of pulp is less than for ground ferrosilicon, i. e. for the same viscosity a greater pulp density can be attained. This might be of importance in future. Adhesionloss is lower for atomized ferrosilicon. The strength of the atomized powder is equal to that of the ground powder.

Ferrosilicon as a Heavy Medium

The use of ferrosilicon powder has risen with the increasing employment of heavy media separation for ores, particularly in the separation of iron ores. In the separation of lead and zinc ores, ferrosilicon is a foreign body and the use of

By | 2018-04-15T05:44:01+00:00 April 15th, 2018|Categories: Gravity Concentration|Comments Off on Ferrosilicon Powder
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