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

Bacteria & Acid Mine Drainage Treatment Method

Objective: To develop an in-mine water treatment system in which bacterial sulfate reduction and limestone dissolution continuously remove metals and acidity from contaminated drainage.

Approach: A section of mine tunnel was converted into a water treatment bioreactor by constructing cinder block dams and filling the area between them with a porous substrate mixture of limestone gravel and compost. Readily fermentable materials such as dairy whey, spent brewing yeast, or sugar were periodically added to the reactor. Mine drainage was impounded behind one of the dams and continuously percolates through the reactor substrate at a controlled rate.

How an Anaerobic Bioreactors Works

The reactor substrate soon becomes anaerobic after it is saturated with mine water. Under anaerobic conditions, sulfate-reducing bacteria consume the organic materials that arc added to the reactor and generate hydrogen sulfide (H2S) and alkalinity. The H2S reacts with dissolved iron and heavy metals to form metal sulfide precipitates. The alkalinity raises the pH of the water and induces aluminum to hydrolyze and precipitate as aluminum hydroxide [Al(OH)3]. Additional alkalinity is generated by the continuous dissolution of the substrate limestone. Metal sulfide precipitates and Al(OH)3 are retained within the reactor, and

By | 2018-03-08T10:43:42+00:00 March 8th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Bacteria & Acid Mine Drainage Treatment Method

Wood Crib Design & Mine Roof Support

Objective: To minimize support costs and to improve ground control by improving wood-crib design and utilisation through the development of engineering methods that will match the placement and performance of the wood cribs to the load conditions imposed by the mine environment.

Background: While wood cribs are used extensively to stabilize mine openings, their utilization is often based on historical practice or trial-and-error rather than on engineering design. This has led to conservative crib utilization where more capacity than is necessary is employed or inadequate capacity is provided when mine conditions worsen. Critical design parameters, such as the stiffness of the support structure, arc often ignored. Optimum crib design and employment is becoming increasingly important as the utilization of wood cribs increase due to the growth of longwall mining, and as the cost of wood continues to rise. A single longwall operation will spend as much as a million dollars per year on the support of the gate roads.

Approach: A model has been developed that predicts wood-crib performance. The model determines the force-displacement relationship for various wood-crib designs through a mathematical equation developed from full-scale testing of

By | 2018-03-08T10:42:54+00:00 March 8th, 2018|Categories: Methods|Tags: |Comments Off on Wood Crib Design & Mine Roof Support

Multiple Seam Longwall Mining Design


Provide longwall operators with practical information and guidelines concerning mine design to reduce problems associated with the interaction of adjacent workings in multiple-seam longwall mines.


The high productivity achieved by longwall mining demonstrates its potential to provide a substantial segment of underground coal production. Longwall mines produce more than 30 pct of underground coal, up from 5 pct just 15 years ago. However, the continued growth of this mining method without appropriate multiple-seam planning may increase the cost and risk of mining. Research by the U.S. Bureau of Mines (USBM) indicates that 25 longwall mines (32 pct of the total number in the United States) have mining in adjacent coalbeds either above or below. About half of these longwall mines report some type of interaction problem with the adjacent workings, such as caving due to subsidence.

Optimization of mine design factors is the best means for controlling interactions between operations in adjacent seams. To avoid higher mining costs, operators should focus on adopting practices and procedures that prevent and control interactions in multiple seams. The USBM, in an effort to improve longwall mine planning, has been investigating multiple-seam

By | 2018-03-08T10:29:57+00:00 March 8th, 2018|Categories: Methods, Mining|Tags: |Comments Off on Multiple Seam Longwall Mining Design

Passive Mine Drainage Treatment Systems

Passive Mine Drainage Treatment Systems provide a low-cost, low-maintenance method for improving mine water quality on abandoned mine land (AML) sites.

Approach: A model (figure 1) is presented for selecting, designing, and sizing one or several passive mine drainage treatment systems that can be used in remediation of AML. The three principal types of passive mine drainage technologies for the treatment of coal mine drainage are an aerobic system, a compost wetland, and an anoxic limestone drain.

The multistep approach presented here provides a simplified method to characterize the type and magnitude of the water quality problem and then to select either a single treatment system or a combination of treatment systems to address the specific site situation.

How a Passive Mine Drainage Treatment System Works

Step 1. Discharge Characterization.

Characterization of the discharge consists of measuring the discharge flow rate and collecting water samples at the point of discharge for chemical analysis. Both the flow rate and chemistry of a discharge can vary seasonally and in response to storm events. It is important to account for this variability by determining flow rates and water chemistry under various conditions.

Water should be analyzed for

By | 2018-03-08T10:27:32+00:00 March 8th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Passive Mine Drainage Treatment Systems

Effect of Oxidation on Flotation of Chromite & Olivine

Chromium and its source mineral chromite are used extensively in stainless steels, high-temperature alloys, chemicals, and high-quality refractories. Significant chromite deposits are found in southwest Oregon and in the Stillwater Complex near Nye, MT. However, chromite is not produced domestically for several reasons. Domestic chromite deposits are relatively small and most are of a lower grade than other resources throughout the world. Most domestic chromite ores also contain silicate gangue minerals that are difficult to remove. Currently, all chromite used in the United States is imported. Typical grades of chromite concentrates used in industry contain 40% to 50% chromium oxide (Cr2O3) and have chromium-to-iron ratio of 1.5:1 to 3:1.

The U.S. Bureau of Mines (USBM) showed that chromite can be selectively concentrated from some low-grade resources by flotation using an amine collector. However, amine flotation is ineffective when the ore contains olivine as the primary gangue mineral. As a result, the technology to treat many domestic chromite ores is lacking.

The possibility of improving chromite beneficiation was indicated by data in the literature. Smith found that oxidizing a domestic chromite at 50 °C for 3 h improved its flotation in the range

By | 2018-03-08T10:17:21+00:00 March 8th, 2018|Categories: Flotation|Tags: |Comments Off on Effect of Oxidation on Flotation of Chromite & Olivine

Impact Cutting Head for Hard Rock Mining

To increase productivity, the mining industry must sometimes try innovative types of mechanized mining systems. In the past, much of this technology has been based on the use of mining machines, such as the road-header, that use rotary cutting heads with drag bits. However, the effectiveness of these machines is limited by rock hardness. If the rock is too hard to be cut by a mining machine, then explosives may be used. Mining with explosives is a labor-intensive operation, and the fracturing and weakening of surrounding rock strata are difficult to control.

Other types of mining machines that can cut in some harder rock use disk cutting bits. However, most of these machines, such as the tunnel borer, are large, difficult to maneuver and limited to cutting entries having a uniform diameter.

A new type of mechanized mining machine has been developed to fill the gap in technology between mechanical cutting machines and explosives or tunnel boring machines. Energy is delivered to an impact cutting head, eight to nine times per second, by a single free-floating piston. With an impact velocity of 10 ft/s, the cutting head is capable of fracturing and

By | 2018-03-08T10:10:41+00:00 March 8th, 2018|Categories: Equipment|Tags: |Comments Off on Impact Cutting Head for Hard Rock Mining


Les concasseurs et le concassage constitue la premiere etape de la comminution. Son objectif n’est pas la liberation des mineraux, mais simplement la reduction de dimension afin de faciliter la manipulation ulterieure du minerai. II est normalement fait a sec en deux ou trois etapes. L’alimentation provient de la mine et a une dimension pouvant aller jusqu’a 1.5 m. Des fois on utilise aussi le concassage comme etape intermediaire dans certains circuits de broyage autogene.

La premiere etape de concassage, qui reduit cette alimentation a 10-20 cm, opere avec le meme horaire que la mine et dans la plupart des cas elle se fait sous terre. Cette operation se fait toujours en circuit ouvert. Le concassage secondaire est toujours accompli au concentrateur, c’est-a-dire en surface. Le produit final, qui servira d’alimentation au circuit de broyage, a une dimension allant jusqu’a 0.5 a 2 cm. L’operation se fait generalement en plus d’une etape et en circuit ferme. Des tamis vibrants sont normalement places en amont des concasseurs afin d’eliminer le materiel assez fin, qui reduirait la capacite de l’appareil, pouvant meme l’etouffer.

Comme mentionne deja, le concassage peut se faire en circuit ferme

By | 2018-03-07T14:01:37+00:00 March 7th, 2018|Categories: Uncategorized|Comments Off on Concasseurs

How to Separate Heavy Rare Earth Elements

Potential increases in overall demand and purity requirements of rare-earth elements (REE) prompted the U.S. Bureau of Mines (USBM) to investigate new technology for separating these elements.

REE, as defined by the USBM, include a group of 17 elements composed of Sc, Y, and the lanthanides. Although exact numbers are not available because of proprietary information, domestic demand for REE in 1993 was estimated to be higher than in 1992. Current market treads are toward high-purity products and away from mixed concentrates; therefore, future supply problems may be encountered if a large demand is developed for one or more of the less abundant REE.

The United States is self-sufficient in light REE resources due to the large REE deposit and processing facility at Mountain Pass, CA, operated by Molycorp, Inc. Separation of the mixed REE, however, is a complicated solvent extraction process involving many mixer-settler units. The Molycorp operation separates Ce from flotation concentrate in a hydrochloric acid (HCl) leach with Ce left in the solid leach residue. An initial solvent extraction on the leach liquor separates La, Nd, and Pr from the heavier REE, which are reprocessed to recover Eu. Another

By | 2018-03-07T12:01:54+00:00 March 7th, 2018|Categories: Hydrometallurgy|Tags: |Comments Off on How to Separate Heavy Rare Earth Elements

Concentrateur Gravimétrique

concentrateur gravimétrique

Concentrateur Knelson

Cet appareil ameliore la separabilite des particules par gravimetrie en travaillant dans un champ centrifuge (60 fois G) plutot que dans le champ de la pesanteur. II comporte un bol de forme conique inversee muni de rainures dans sa parois interne (pour retenir les particules) et qui tourne a un vitesse tres elevee (1200 rpm). L’alimentation de particules, normalement assez grossieres, est injectee au centre de l’appareil d’ou la force centrifuge developpee les envoie vers les parois. De l’eau est injectee a travers des trous pratiques dans la parois afin de repousser vers le centre les particules de masse volumique plus faible evitant aussi la formation d’un lit compact de particules sur la parois. De cette facon, meme les particules lourdes tres fines seraient capables d’acceder la parois suite a l’action de la force centrifuge. Les particules lourdes (par exemple d’or) restent done emprisonnees dans les rainures, d’ou elles sont enlevees lors de l’arret de l’unite, apres quelque temps d’operation.

Le concentrateur peut etre equipe avec un systeme de decharge automatique, dont l’action de lavage necessite d’environs deux minutes,

By | 2018-03-07T15:34:40+00:00 March 7th, 2018|Categories: Gravity Concentration|Comments Off on Concentrateur Gravimétrique

Table a Secousses

Principe de fonctionnement de la Table a Secousses: Lorsqu’un film d’eau coule sur une surface plate inclinee, l’eau pres de la surface est retardee par la friction. La vitesse augmente vers la surface libre de l’eau. Si des particules de minerai sont introduites dans l’eau, les particules plus petites ne se deplacent pas aussi vite que celles plus grandes, puisqu’elles sont submergees dans la partie plus lente du film. En meme temps, les particules plus lourdes seront moins entrainees que les particules plus legeres (figure ci-dessous). Ainsi, une nette separation se produira entre des particules grossieres et legeres et particules petites et lourdes. Ce type de separation est exploite dans les tables a secousses, peut etre le separateur le plus parfait qu’il existe.


Elles consistent en une table inclinee, en longueur et en largeur. L’alimentation, suspension a environ 25% en solides, est introduite dans le coin le plus eleve (voir figure suivante). De l’eau de lavage est introduite aussi du cote de l’alimentation. La table est secouee en sa longueur, avec un mouvement en avant lent et vers 1’arriere tres rapide. Cette action

By | 2018-03-11T12:41:49+00:00 March 7th, 2018|Categories: Gravity Concentration|Tags: |Comments Off on Table a Secousses
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