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

Recycling of Stainless & Speciality Steel

To reuse chromium, nickel, and molybdenum now lost in stainless and specialty steel-making wastes, and simultaneously to overcome the current environmental problem resulting from landfilling these wastes. A variety of stainless and specialty steelmaking wastes are agglomerated and recharged into the plant’s electric arc furnaces.

How It Works

Stainless and specialty steel-making wastes such as bag-house dust from the electric arc furnace, dust from the argon-oxygen decarburization unit, grinding swarf, and mill scale are blended in proportion to the ratio in which they are generated. Next they are agglomerated on a pelletizer with an addition of a small amount of carbonaceous reducing agent, and air-dried in preparation for being recharged into the furnace. Some mixtures of wastes tested in the laboratory required the addition of binders and/or the use of ovens in lieu of air-drying to produce sufficient pellet strength. Although the optimal maximum particle size of wastes being pelletized is 35 mesh, somewhat larger particle sizes were satisfactorily pelletized during in-plant tests. The photograph shows a typical mixture of wastes and the pellets made from them.

recycling stainless steel

The pellets made from wastes can be charged to the electric arc furnace as 5

By | 2017-08-22T14:13:11+00:00 August 22nd, 2017|Categories: Electrometallurgy|Tags: |Comments Off on Recycling of Stainless & Speciality Steel

Hydrogen Chloride Crystallization of Aluminum Chloride Hexahydrate

As part of its effort to produce cell-grade alumina from clay, the Bureau of Mines investigated the hydrogen chloride gas-sparging crystallization of aluminum chloride hexahydrate (ACH) from aluminum chloride liquor, to provide information for optimizing the crystallization operation.

Four parameters important in controlling the crystallization of the aluminum chloride hexahydrate and the concentration of impurities, particularly phosphorus and magnesium, in ACH crystals are (1) aluminum chloride concentration in the feed solution to crystallization, (2) hydrogen chloride gas flow rate, (3) temperature, and (4) concentration of phosphorus and magnesium also in the feed solution. Parameters 1, 2, and 3 affect crystal formation. The combined effects are very important because the phosphorus and magnesium concentrate in the crystals during the early stages of crystal growth.

Aluminum chloride hexahydrate of cell-grade purity was crystallized from saturated aluminum chloride solutions containing less than 0.003 wt-pct P2O5 and 0.010 wt-pct MgO. Crystallization temperatures less than 60° C decreased crystal purity.

Bauxite, 93 pct of which is imported to the United States, is the only raw material used domestically for the production of alumina. As part of its effort to reduce U.S. dependence on foreign resources, the Bureau of Mines is investigating the use of domestic aluminous resources for

By | 2017-08-22T14:10:21+00:00 August 22nd, 2017|Categories: Electrometallurgy|Tags: |Comments Off on Hydrogen Chloride Crystallization of Aluminum Chloride Hexahydrate

Dust Controlling Water Sprays

High-pressure shrouded sprays were first tested on a bench to determine air-moving capability and dust collection efficiency. The bench-scale tests indicated that at 500 psi and above, the dust collection efficiency, when sampled downstream of a water eliminator, was about 99 pct for two types of nozzles. However, for the same water flow, the induced airflow was about three times greater in one type than in another. Since the only difference in the nozzles was the spray angle, this factor was important in air movement through a shrouded spray.

Full-scale model mine tests were then conducted to determine the reduction in dust concentration behind the line curtain and at the operator position produced by high-pressure sprays in a shroud. The shroud was mounted on top of the boom of a model continuous miner, and high-pressure (greater than 500 psi) sprays were installed inside the shroud. The inlet of dusty air to the shroud was open toward the face and the outlet toward the exhaust line curtain. The high-pressure sprays were compared with conventional sprays mounted at the head of the continuous miner and directing water toward the face. The difference at the operator position (opposite side of brattice) was significant in

By | 2017-08-21T17:10:59+00:00 August 21st, 2017|Categories: Environment & Tailings|Tags: |Comments Off on Dust Controlling Water Sprays

Heap Leaching Gold & Silver Ores

An investigation of a particle agglomeration technique as a means of increasing the percolation rate of leaching solutions through heaps of clayey or finely crushed, low-grade, gold and silver ores. Bench-scale and pilot-scale experiments conducted on different ores indicated that the percolation rate of cyanide leaching solution was enhanced markedly by mixing the ore with a binder, such as lime or Portland cement, moistening the mixture, then mechanically agglomerating and aging the feed prior to heap building and leaching. In addition, the rate of silver and gold extraction markedly increased without sacrificing total recovery of values. The use of concentrated cyanide solution instead of water during the agglomeration procedure substantially decreased the leaching time required to obtain maximum recovery. Results from bench-scale and pilot-scale experiments using the particle agglomeration technique are discussed.

Exploration during the past few years has identified numerous low-grade, gold-silver deposits throughout the Western United States. Recent increases in gold and silver prices have generated a great deal of interest in processing these low-grade ores by heap leaching. Heap leaching with cyanide has potential application to many of these low-grade materials; however, if heap leaching is to be successful, the material must maintain good permeability after being stacked

By | 2017-08-20T12:36:39+00:00 August 20th, 2017|Categories: Hydrometallurgy|Tags: |Comments Off on Heap Leaching Gold & Silver Ores

Copper Cementation System for Small Scale Mining Operations

We studied the precipitation of copper from dilute acidic sulfate solutions using shredded automobile scrap in a rotary drum. The tests established that the scrap in the rotary drum precipitated copper faster and more completely than shredded, detinned, tinplate scrap in a launder, with comparable iron consumption. Although power is required to rotate the drum, the faster precipitation and continuous recovery of cement copper are advantages of the tumbler method. Cost evaluation indicates that the rotary drum method, which uses relatively low-cost and readily available shredded automobile scrap, is competitive with the launder method, which uses relatively high-cost shredded tinplate scrap or detinned shredded cans.

The first recorded domestic production of cement copper was 8,200 tons in 1921. By 1967 production had expanded to about 200,000 tons annually. Presently, about 300,000 tons of shredded tin cans and tinplate scrap are used annually for the production of cement copper. New facilities to leach porphyry mine waste dumps will further increase production in the near future.

Two methods are used in current cementation practice. The first method consists of passing acidic copper-bearing leach solutions through launders containing shredded tin cans. The second method, developed by Kennecott Corp., uses shredded and detinned cans and tinplate

By | 2017-08-20T10:46:25+00:00 August 17th, 2017|Categories: Electrometallurgy, Hydrometallurgy, Smelting - Melting - Refining|Comments Off on Copper Cementation System for Small Scale Mining Operations

Zinc Chloride & Electrowinning

To help assure an ample domestic supply of zinc and other essential minerals which provide the foundation of the Nation’s economy and security, the Bureau of Mines is investigating an aqueous chlorine-oxygen leaching procedure to produce zinc chloride from complex sulfide concentrates and is also studying methods of fused-salt electrolysis to produce special-high-grade zinc metal from the resulting purified zinc chloride.

Lead-zinc ores are often difficult to treat by conventional processes because the galena and sphalerite minerals contain interlocked pyrite and copper sulfide minerals. When these ores are processed by flotation, the resulting zinc concentrate has a complex composition. If the flotation circuit is operated to produce a better grade of zinc sulfide concentrate, zinc losses are typically high and overall recoveries are very low. Examples of these types of material are the Copperhill deposit in Tennessee and the Crandon deposit in Wisconsin.

Conventional smelting practice is not suited for the recovery of metal values from these complex sulfide concentrates; therefore, the Bureau of Mines is investigating a hydrometallurgical process to provide a more effective means to utilize these resources. Studies have been conducted and previously reported on a chlorine-oxygen leaching system for extracting metal values from these concentrates, which are complex

By | 2017-08-11T09:34:04+00:00 August 11th, 2017|Categories: Electrometallurgy|Tags: |Comments Off on Zinc Chloride & Electrowinning

Nickel & Cobalt Electrowinning

As part of the goal to develop technology that can meet critical and strategic needs of minerals and metals, the Bureau of Mines is investigating a procedure for selectively extracting nickel, cobalt, and copper from low-grade domestic laterites. Although the Nation produces less than 10 pct of the primary nickel it consumes and essentially none of its cobalt, extensive resources exist in southern Oregon and northern California containing 0.5 to 1.2 pct Ni, 0.06 to 0.26 pct Co, and about 0.01 to 0.05 pct Cu. These resources are amenable to processing by the Bureau of Mines procedure, for which the results of initial studies regarding characterization of the deposits and development of preliminary process parameters and conditions have been reported. Production would help offset increasing dependence for these strategic and critical metals on foreign suppliers.

An engineering feasibility study and cost evaluation of a commercial size plant has been completed. More extensive pilot plant work is being done. The procedure includes

  1. Reduction roasting of ground, dry, pelletized laterite with carbon monoxide in a multiple-hearth furnace at about 600° C.
  2. Leaching the product in ammoniacal-ammonium sulfate liquor with oxygen to extract metal values as soluble amine complexes.
  3. Solid-liquid separation followed by precipitation
By | 2017-08-11T09:32:07+00:00 August 11th, 2017|Categories: Electrometallurgy|Tags: |Comments Off on Nickel & Cobalt Electrowinning

Recover Scrap Battery Lead by Electrolysis

One objective is the secondary recovery of metals, minerals, and other values from waste products and the development of uses for them. In line with this objective, research was initiated to develop an environmentally acceptable alternative to the pyrometallurgical processes currently used by the secondary lead industry. These processes produce 45 pct of this country’s needs. The majority of the metal supplied to secondary lead smelters is in the form of scrap lead-acid batteries. The lead metal and the sludge are separated from the case and the electrolyte and are smelted at high temperatures in a reverberatory or blast furnace. Emissions of lead and sulfur oxide fumes during pyrometallurgical smelting are very difficult to control, making it virtually impossible for the industry to meet the emission standards recently promulgated by the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA). Officials from industry and EPA estimate that strict enforcement of the new standards will result in the closing of more than 90 pct of the secondary lead smelters in the United States.

The smelters have an additional burden to produce a product that is purer than ever before for use in the new maintenance-free (MF) batteries.

Work at the

By | 2017-08-10T11:17:37+00:00 August 10th, 2017|Categories: Hydrometallurgy|Tags: |Comments Off on Recover Scrap Battery Lead by Electrolysis

Micro-Diffusion Photo-Metric Technique of Free Cyanide Determination

Microdiffusion Procedure: For the samples preserved at pH >12, take a 10-ml aliquot and determine the volume of 0.5M KH2PO4 necessary to adjust the pH to 7.0 ±0.1 using microliter pipets and a pH meter.

Lubricate the outer rim of a Conway micro-diffusion dish (Corning Cat. No. 3135) with silicone stopcock grease to effect a gas-tight seal with the cover. Add 3.00 ml of 0.1M KOH to the center section. Pipet 10.00 ml of sample into the outer chamber. Using a variable volume microliter pipet, add the volume of 0.5M KH2PO4, necessary to attain pH 7.0. Immediately stir the sample solution with a plastic rod and seal the dish with the cover. Place the dish in the dark, and allow it to stand overnight.


Stock KCN Solution, 1 mg CN-/ml. Dissolve 1.25 grams of reagent grade KCN in 0.1M KOH. Transfer to a 500-ml volumetric flask and dilute to volume with 0.1M KOH. Store in a plastic bottle. Standardize weekly with 0.0192N AgNO3 using rhodanine indicator.

Dilute KCN Solution, 0.01 mg CN-/ml. Pipet 500 ul of stock KCN into a 50-ml volumetric flask. Dilute to volume with 0.1M KOH. Prepare fresh daily.

Standard 0.0192 AgNO3 Solution. Dissolve 5.265 grams of 40°C-dried AgNO3 in water,

By | 2017-08-08T11:48:56+00:00 August 8th, 2017|Categories: Assaying, Laboratory Procedures|Tags: |Comments Off on Micro-Diffusion Photo-Metric Technique of Free Cyanide Determination

Recover Copper in Smelter Dust

The Bureau of Mines researched methods for recovering copper from cyclone and electrostatic-precipitator dusts of primary copper smelters as part of its program to maximize minerals and metals recovery from primary and secondary domestic resources.

Small-scale studies showed that use of 110 pct stoichiometric sulfur and 123 pct stoichiometric carbon, based on producing a 40-pct copper-iron matte, resulted in the recovery of 95 pct of the copper contained in the dust. Typical mattes contained less than 10 pct of the arsenic, 30 pct of the bismuth, and 45 pct of the antimony and tin contained in the dust. Matte was converted to blister copper by injecting up to 200 pct of the stoichiometric oxygen requirement over a period of 2 to 3 hours. Up to 76 pct of the copper contained in the dust was recovered as a crude blister copper containing about 2 pct arsenic, 0.5 pct antimony, and less than 0.1 pct bismuth and tin.

A matte-white metal product resulted from carbothermically reducing dust with coal, lime, and silica. Up to 95 pct of the copper was recovered in the combined product.

Direct carbothermic reduction and matte smelting were two pyrometallurgical techniques investigated by the Bureau of Mines on a small

By | 2017-08-05T09:24:30+00:00 August 5th, 2017|Categories: Smelting - Melting - Refining|Tags: |Comments Off on Recover Copper in Smelter Dust