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

Electrorefining Calcium Metal Electrowinning

The U.S. Bureau of Mines developed an alternative electrochemical process for the production of calcium metal. The current industrial practice is costly, complex, and inefficient. The Bureau method involved electrowinning of a calcium-tin alloy followed by electrorefining to produce calcium metal. In the electrowinning cell, CaCl2 was fed to a KCl2-CaCl2 electrolyte. The calcium was electrowon at 650° C into the pure molten tin cathode until the cathode contained 7.5 wt pct Ca. Current efficiency for electrowinning averaged over 90 pct. The resulting calcium-tin alloy served as the anode for the electrorefining cell, which employed a CaCl2-CaF2 fused salt as the electrolyte. Calcium metal was electrorefined at 850° C with a current efficiency of 85 pct based on calcium metal recovered. The calcium metal analyzed 99.2 pct, which is purer than commercially produced calcium.

The U.S. Bureau of Mines has investigated the electrolytic production of calcium metal. The procedure has low energy requirements and may lower the cost of producing calcium. Lower cost calcium metal would promote wider use.

Before adoption of the present commercial process, calcium metal was manufactured by the direct electrolysis of CaCl2. In this batch process, a “carrot” of solid calcium was electrowon that contained a large amount

By | 2017-10-21T13:10:23+00:00 October 21st, 2017|Categories: Electrometallurgy|Tags: |Comments Off on Electrorefining Calcium Metal Electrowinning

Column Flotation Testing Better & Improved Recovery

We investigated column flotation for recovery of a high-grade fluorite (CaF2) concentrate and byproduct concentrates from the Fish Creek fluorite deposit in Eureka County, NV. The recovery scheme consisted of (1) grinding the ore to minus 48 mesh, (2) fluorite rougher and cleaner flotation, (3) desliming the rougher fluorite flotation tailings at 20 µm, (4) mica flotation, and (5) silicate rougher flotation. Acid-grade fluorspar, mica, free silica (SiO2) sand, and low-grade beryl (Be3Al2Si6O18) concentrate were produced in a 100 lb/h continuous column flotation unit (CCFU). The highest results achieved were 96.6-pct CaF2 recovery in a first cleaner concentrate containing 99.7 pct CaF2. Beryl recovery was as high as 92 pct at a grade of 5.3 pct BeO. The silica sand, which assayed 98 pct SiO2, was recovered as the rougher beryl flotation tailings. Collector reagent consumption was reduced 45 pct for fluorite and 58 pct for silicate flotation in comparison with bench-scale conventional flotation. All products were significantly improved in both grade and recovery over conventional flotation results, and the recovery scheme was simplified by removal of several stages of flotation in the fluorite and silicate flotation steps.


Fluorspar, the commercial name for the mineral fluorite, defines material that

By | 2017-10-21T10:55:49+00:00 October 21st, 2017|Categories: Flotation|Tags: |Comments Off on Column Flotation Testing Better & Improved Recovery

How to Recover Chromite

The USBM conducted laboratory research including operating a nominal 100 lb/h pilot plant to demonstrate the recovery and concentration of chromite by gravity and flotation operations. Gravity beneficiation test results show that concentrates contained as much as 52 pct chromic oxide (Cr2O3) with recoveries of about 80 pct. Results from the bench-scale unit operations of mineral liberation, tabling, vanning, spiraling, pinch sluice, work index, and thickener area determination tests are presented in this report.

The United States is highly dependent on imported materials for many mineral products that are critical to its economy and defense capabilities. Chromium is an important example. Apparent annual consumption of chromium-containing materials is on the order of 400,000 mt of contained chromium metal. However, domestic production has occurred only sporadically, mostly in times of national emergency, and none has been produced since 1962. The U.S. Bureau of Mines is investigating the potential for processing domestic ores as part of a program to develop technology for increasing production of mineral products from U.S. sources.

Resources of chromium in the conterminous 48 States are currently estimated to consist of 450 million mt of ore with Cr2O3 grades ranging from 0.7 to 42.9 pct and averaging

By | 2017-10-21T08:55:29+00:00 October 21st, 2017|Categories: Gravity Concentration|Tags: |Comments Off on How to Recover Chromite

Ground Sluicing Operations

The mines described are the larger ones and a few typical small ones visited by the authors in 1932. Comparable data concerning them were shown in table 7.


Richard Leoncavallo was working a pit on the Morgan placer on Clear Creek below Blackhawk, Colo., in July 1932. The gravel was tight, coated with clay, and overlain by 2 or 3 feet of recent wash and mill tailings. Cuts about 6 feet wide radiated from the head of the sluice boxes, following rich streaks on a false clay bedrock. All the gravel had to be loosened by picking, which was done while the water was running over the face of the cut. Boulders more than 6 inches in diameter were thrown out by hand. Some of the gravel near the head of the sluice was shoveled in by hand.

About 70 miner’s inches of water was used; some of the sediment in the creek water was settled out in a small reservoir above the mine. The sluice consisted of two 10-foot boxes 18 inches wide and 12 inches deep having a grade of 12 inches per box. The first 4 feet was floored with 1-inch screen placed tight on the bottom of the

By | 2017-10-20T11:26:08+00:00 October 20th, 2017|Categories: Gravity Concentration|Comments Off on Ground Sluicing Operations

Sulfide Ore Treatment Gold – Silver – Copper – Cobalt – Zinc Recovery

A procedure was developed for recovering gold, silver, cobalt, copper, and zinc from a massive sulfide ore by a hydro-metallurgical process. The procedure consists of (1) oxygen pressure leaching; (2) iron, arsenic, and copper removal from the leach solution by precipitation; (3) selective extraction of cobalt and zinc from solution; (4) electro-deposition of the cobalt and zinc from the strip liquor; and (5) cyanidation of the pressure leach residue to recover gold and silver. The results are discussed in terms of efficiency of metal recovery and conclusions drawn as to possible benefits and broad applications of the process.


Ores that contain sulfide minerals are important resources for many of these vital commodities. Sulfide minerals are common forms for the strategic and critical metals cobalt and nickel.

Metallurgical processing of sulfide minerals can be complex because the minerals normally contain several associated metals. Cobalt and nickel ores usually contain copper, which can be present in a variety of forms, or other common metals; the cobalt and nickel are typically minor values. Lead, zinc, and copper are often associated with each other. Also, gold and silver are commonly associated with those base metals. Mineral recovery procedures must therefore deal with several metals

By | 2017-10-20T10:57:32+00:00 October 20th, 2017|Categories: Hydrometallurgy|Tags: , , , , , |Comments Off on Sulfide Ore Treatment Gold – Silver – Copper – Cobalt – Zinc Recovery

Gold Sulphide Ore Oxidation by Alkaline Pressure

The U.S. Bureau of Mines developed an alkaline oxidative pretreatment to increase the recovery of gold from refractory sulfide ores containing arsenopyrite (FeAsS) and/or pyrite (FeS2). Pretreatment of a low grade ore containing 0.4% FeAsS, 3.5% FeS2, and 2.74g/mt Au with 1.2M NaOH, 40 psig 02, 100° C, and 4 hr in a 2-L autoclave resulted in 94 to 96% sulfide oxidation. Cyanidation of the pretreated residue resulted in 88% Au extraction compared to <20% Au extraction for untreated ore. Cyanide consumption was 0.25 kg NaCN per metric ton of ore. A flowsheet for treating sulfidic low-grade gold ore is proposed.

During the 1980’s, the gold industry saw strong gold prices precipitating what is termed the “gold rush of the 80s.” The increased activity has resulted in processing of ores previously considered not profitable or those classified as refractory. Refractory ores, such as ores with gold disseminated in pyrite or arsenopyrite, are not amenable to direct cyanidation.

Historically, refractory ores were roasted to oxidize the sulfides. New hydrometallurgical technology developed in the past decade such as aqueous pressure oxidation (Berezowsky, 1984) and bacterial oxidation (Bruynesteyn, 1984) are viable alternatives to roasting.

Oxidation of sulfides from a thermodynamic point of view is feasible

By | 2017-10-20T11:02:56+00:00 October 20th, 2017|Categories: Hydrometallurgy|Tags: |Comments Off on Gold Sulphide Ore Oxidation by Alkaline Pressure

Iron Oxide Pellets

Develop methods of enhancing and measuring the high-temperature softening and melting properties of iron oxide pellets reduced under simulated blast furnace smelting conditions.

Add dolomite and limestone flux and a low-cost organic binder, such as starch, carboxyl methylcellose (CMC), or waste papermill sludge, to the iron oxide concentrate to produce hematite (ferric oxide) pellets with superior high- temperature metallurgical properties. Simultaneous increases in softening temperature, gas permeabilily, and enhanced metallization rates are sought to improve blast furnace productivity and energy efficiency.

In the past, bentonite, an inorganic binder, was the only additive (binder) used in the production of pellets made from iron ore concentrate. Research has shown that the reducibility of conventional (acid) pellets can be increased by the addition of flux or an organic binder. The increase in pellet reducibility results in less wustite in the center of the pellet at high temperatures, such as those obtained in the cohesive zone of the blast furnace.

Design Procedure

The Bureau has constructed a high-temperature, softening-melting testing apparatus for evaluating the behavior of pellets under simulated blast furnace conditions. This apparatus is very effective in evaluating the contraction and pressure drop of fired pellets made with different additives, such as flux, bentonite, CMC,

By | 2017-10-20T11:21:51+00:00 October 20th, 2017|Categories: Pyrometallurgy, Smelting - Melting - Refining|Tags: |Comments Off on Iron Oxide Pellets

Sluicing VS Rock Boulders & Bedrock

How to Handle Rock Boulders when Sluicing

Boulder,’s generally are handled in ground-sluice mines in the same manner as in hydraulic pits. Derricks are the commonest mechanical device used for the purpose. (See fig. 8). These may be operated by a hand winch or by steam, gasoline, or electric power. In wide deposits boulders may be removed on platform-skips operated on a cableway. At the Harvey placer, where the ground contains an unusually high percentage of boulders (35 percent over 6 inches in diameter), two hand-operated derricks are used in a pit 90 feet wide. At the Osborne lease a steam-operated derrick is employed. At the other ground-sluice mines listed boulders are moved by hand; large ones are blasted. At the Osborne lease large boulders are drilled with jackhammers, using steam from the boiler which supplies power for operating the derrick. Boulders too large to move by hand are blown from the pit by explosives at the Camp Bird mine.

Bringing the ground-sluice water over the face of the pit has a decided advantage in that boulders need to be handled only once. They are either moved completely out of the workings or piled in the pit on cleaned bedrock,

By | 2017-10-20T11:31:56+00:00 October 20th, 2017|Categories: Gravity Concentration|Tags: |Comments Off on Sluicing VS Rock Boulders & Bedrock

Laboratory Zadra Electrolytic Cell

A ZADRA electrolytic cell adapted to strip gold from sulfide solutions thereof which comprises a cathode assembly having a vertical metallic pipe adapted to deliver gold-bearing solution to the cell and to serve as a negative bus bar for delivering electric current to said cell, said pipe being axially positioned in said cell and being provided near its lower end with an aperture for permitting egress of solution from said pipe into said cell, a radially-extending metallic plate fastened to said pipe at its lower end, a plurality of upwardly extending wire rods spaced about said pipe and fastened at their lower ends to said plate for distributing electric current about said pipe, a non-conductive perforated basket enclosing the pipe, plate and rods to restrain solids while permitting fluid flow, said basket being adapted to contain charred excelsior cathode material in contact with said rods; a perforated anode surrounding said cathode assembly adapted to permit flow of solution through said anode perforations, a weir cup surrounding said anode and said cathode assembly for controlling solution level overflowing said cup, and a launder adapted to collect overflow of stripped solution from said weir cup.

A Homemade DIY Zadra Electrolytic Cell

By | 2017-10-20T10:37:39+00:00 October 20th, 2017|Categories: Electrometallurgy|Comments Off on Laboratory Zadra Electrolytic Cell

Placer Mining Equipment

Specific Placer mining equipment is needed for each of the methods which can be classified according to the several methods of excavating and transporting the gravel, or they may be designated to correspond with the various ways of saving the gold. The actual moving of the gravel from place is always the principal concern of the miner, and often the gold-saving is entirely incidental to the working of the deposit. The following classification, therefore, seems the most logical and is the one generally used by placer miners:

  1. Hand-shoveling;
  2. ground-sluicing;
  3. hydraulicking;
  4. excavating by teams or power equipment;
  5. dredging;
  6. drift-mining.

Combinations of methods 1, 2, 3, and 4 may be used, and one method may graduate into another. The methods may be defined as follows:

Hand-shoveling.- Hand-shoveling comprises picking and shoveling surface-placer gravels and washing the material excavated to recover the valuable minerals. The gravel may be washed at the “diggings” or transported by wheelbarrows, pack animals, carts, or trucks to the nearest available water. The general method of excavating varies little, but it may be subdivided according to the method of washing the gravel: (a) Panning; (b) rocking; (c) use of long torn; (d) shoveling into boxes (sluicing); and (e) dry washing.


By | 2017-10-19T11:38:06+00:00 October 19th, 2017|Categories: Gravity Concentration|Tags: |Comments Off on Placer Mining Equipment
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