L David Michaud

About David Michaud

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 https://www.911metallurgist.com/about-us/

Spent Alumina Regeneration

Regeneration of the spent alumina was accomplished by using 0.25% NaOH and 0.5% NaOH. Figure 11 shows the release of selenium, silica, and aluminum when regenerating the adsorption columns that had received the mine leachate. In this case, the regeneration was performed in an upflow mode using 30% bed expansion. As expected, the losses of aluminum during regeneration

alumina-adsorption release of se

increased with increasing NaOH strength. These results indicated that the removal of silica and selenium from the spent material was possible by using a NaOH concentrations as low as 0.25%. More selenium was released from fixed-bed columns receiving synthetic selenite solutions than from columns receiving synthetic solutions. Batch regeneration tests indicated that similar release of selenium could be accomplished with one hour of contact with a 0.25 % NaOH solution.

Kaolin Ceramics

clay-minerals magnetic separator

Kaolin is a clay comprised essentially of the mineral kaolinite which has the oxide composition of 46.3% SiO2, 39.8% Al2O3, and 13.9% combined H2O. The structural formula of kaolinite is (OH)8Si4Al4O10. These deposits are sedimentary and contain approximately 90% or more kaolinite along with minor quantities of quartz, mica, and smectite along with trace quantities of ilmenite, anatase, rutile, goethite, zircon, tourmaline, and kyanite. For many uses these accessory and minor minerals must be essentially removed or greatly reduced in amount. The most efficient way to remove these impurities is a wet process, the essential steps of which are shown in Figure 1.

Generally the quartz and mica are present as particles that are coarser than 44 microns (325 mesh) and can be removed by gravity settling and screening. Particle size separations are accomplished by using continuous centrifuges which can separate the kaolin particles into fine and coarse fractions. The particle size of the fine fractions can be controlled between about 70% finer than 2 microns to essentially 100% finer than 2 microns. Any quartz and mica particles that are finer than 44 microns will be contained in the coarse fraction. High intensity ….Read more

How to Derate a Pump Curve for Slurry Pumping

The pump curves published by pump manufacturers are for the performance of the pump on water. Some pump manufacturers use a derating factor to correct the head and efficiency of the pump when pumping slurry.

This a subject which has had a lot of controversy and disagreement It is suggested that the method used be left to the manufacturer The method they use works for them.

As a final check, another factor in the selection of the pump size is the entrance or suction velocity The higher the entrance velocity the higher the wear rate will be on the leading edge of the impeller vanes and the impeller eye. Generally speaking, eye velocities below 15 or 16 ft./sec. are preferred. The velocity must be high enough to insure that the slurry and solids reach the impeller eye, but not so high to cause rapid wear.

Now that we have looked at the parameters which affect the selection and sizing of a pump, let’s take a set of conditions that we have derived by the testing and careful analysis of the system or as supplied by the customer to select a pump:

Flow: 4000 GPM – Mill Discharge Service
Head: 100 ft.
Sp gr of ….Read more

Silver Chloride Chemistry

To appreciate the development of industrial silver chloride processing it is helpful to outline some of its general properties. Since more comprehensive reviews are available, only basic concepts will be covered here.

Silver chloride is a white, curdy, crystalline solid compound. In the lab, it is prepared from a solution of AgNO3 by precipitation with NaCl solution. It is roughly 75% silver by weight. Silver chloride melts at a temperature of 455° C and boils at 1550° C. It is one of the few chloride compounds known to be very insoluble in water. Only PbCl2 and Hg2CL2 share this unique property, with PbCl2 being soluble in hot water. Thus, selective precipitation of silver from a mixed metal ion solution is an ideal method. Upon precipitating, silver chloride tends to agglomerate into larger and larger masses. This is enhanced by mild agitation. For improving solid settling rates and obtaining clear resultant filtrate solutions from liquid/solid separations, this agglomeration enhancement principle is important.

Electrochemically, AgCl is quite noble. The standard potential relative to hydrogen is 0.2223 V for the following reaction.

AgCl (S) + e- → Ag° + Cl-…………………………………………………(1)

As such, it may be reduced by redox couples with many less noble materials. This knowledge ….Read more

Effect of Air Flowrate on Flotation Column

On a flotation column cell, the variation of concentrate flowrate, clean coal yield and product grade with air flow rate are shown in Figure 4. These tests were carried out using a 5 wt. % feed slurry. The results show that the concentrate flow rate, yield and product ash content increased with air flow rate. This trend is expected since the available bubble surface area increases with air flow rate. For solid feed rate in the range 240-320 g/min, it appears that conditions of free flotation are encountered at air flowrates above 3 LPM. This is consistent with our earlier observation on the presence of air bubbles in the tailing samples collected at low air flowrates. Since the project objective called for the production of clean coal with an ash content of 5%, our results suggest that a single column flotation stage is sufficient for the beneficiation of the Lower Kittaning seam coal at yields of 66-80%.

flotation column variation of concentrate product

Evaluation of Vortactor Turbulent Contactor

The Mott porous sparger used in the studies reported above was replaced with the Vortactor. Table 1 shows the preliminary results obtained with the Vortactor ….Read more

Visman’ General Sampling Theory

A comprehensive analysis of the entire range of related studies would require a lengthy discussion. Instead, this paper will focus only on the work of Visman (1962, 1969), because his work is part of the current ASTM D2234 standard on coal sampling (American Society for Testing and Materials, 1985). Visman’s work attempts to empirically determine a formula for sampling error. Visman has called this work “a general sampling theory“. The theory is intended for both stationary and moving streams of heterogeneous material. Two sets of increments are taken: one set of small increments and one set of large increments. Each increment is analyzed separately. Two constants A and B are estimated and used in the empirical formula for the variance between increments of a given size W:

σ²I(w) = A/W + (1 – 1/W)B.

Here A represents the “random variance” and B the “segregation variance”. Visman uses a “sampling board” to simulate sampling from populations with various degrees of segregation.

Duncan (1971) shows that this empirical formula can be approximately deduced theoretically, and further that

B = pA

where p is the correlation between increments of the same size. Duncan (1971) points out that the formula is only strictly valid ….Read more

How to Reduce Ball Mill Overload Risk

Two different circumstances must be addressed for the reduction or elimination of overload risk: a) in existing operations, or b) in the design of new grinding circuits. The methods necessary are in the first case an adjustment of operating conditions; and in the second an adjustment of mill shapes.

Existing Operations: from Equation (1) for mill power with a system of fixed dimensions, power input, and ore properties, Equation (8) follows:

Fc (1 – Lf) Lf = C1………………………………………………………………(8)

The axial velocity equation at overload (Table 3) can be changed to:

Vax = C2/[0.50 – 0.66 Lf]………………………………………………………(9)

dimensionality in ball mill dynamics

With C2 determined by use of the Lf value at overload. As shown in Table 4, it is then possible to assume values for Vax/Vax to represent degrees of axial velocity reduction, along with lower values for Lf, and calculate the values of Fc necessary to hold power constant. The mill operating data in Table 2 show that at the already low Lf value for Lornex, little if any practical overload risk reduction is likely by this means. On the other hand, Sierrita’s Lf value of 0.48 suggests that major reductions in risk ….Read more

Column Flotation BIAS

Counter Current flow of mineralized bubbles & wash water

The column underflow is always of slightly higher volume than the feed. This volume imbalance, called BIAS in the control system, is made up by wash water inserted at the top of the column. Part of this wash water travels down the column to exit with the underflow. The remainder overflows with the loaded bubbles.

It is this unique application of wash water that completely separates the column method of concentration from anything that has been used before. A conventional, draining froth bed is NOT used in the column.

The regular flotation cell uses a draining froth bed to separate values and gangue (Fig. 2). As the flotation bubble, carrying its mineralized load, arrives at the interface it is surrounded by a relatively large wall of slurry containing gangue. In moving upward into the froth bed, the slurry around the bubble tends to drain back beneath the interface. This draining brings the bubbles closer together and they start acting like a mechanical filter, entraining some of the gangue particles.

Apart from these entrained particles, there is another source of contamination. The water in the froth product of a cell is feed water and ….Read more

Gold Refining Contract

The operator’s relationship with the refinery depends entirely upon a well-defined written contract, good representation at the refinery and the use of reliable assay laboratories. While all contracts are similar in that they are meant to safeguard the interest of both refiner and miner, it is not unusual to find a single refinery writing a variety of contracts, each one responsive to the special needs of different mines.

Mine outturn can either be sold outright to the refiner or be “tolled” through the refinery. In the latter case, the refiner will process the shipment for a fee and return an agreed upon percentage of metals in the dore to the mine in a specific form (kilobar, 100 ounce bar, etc.) at a specified time and location. Contracts can also cover the sale of a single shipment or cover multiple batches of mine outturns for a period of time, typically one year. A long term contract provides more benefits for the miner than a single sale because the refinery will generally offer a volume discount. However, at times when many refiners are operating below capacity, a refiner may offer a “special” discount price for a single sale. This is usually the exception ….Read more

Gallium Uses

Gallium: Cominco has been at the interface between the semiconductor materials and the components industries since the commercialization of the transistor in the early fifties. Based on our commitment to R&D, we have become the largest merchant supplier of several specialty semiconductor substrates including LEC-grown semi-insulating gallium arsenide wafers on this continent.

The following remarks are an attempt to project from this position the potential impact of several advanced uses on the demand for gallium in terms of quantity and quality for the next 10-15 years. This information will be useful in guiding the extractive metallurgical industry in both capital investment and R&D strategy.

Over the past three or four years, it has been practically impossible to escape the hype about the potential of gallium arsenide in our information society, as can be seen in Figure 1.

Scientists have recognized long ago that gallium arsenide has several properties which make it a superior semiconductor material compared to silicon. Table 3 shows some of the positive features frequently cited.

Drawbacks of SI GaAs substrates compared to silicon are shown in Table 4. None of these drawbacks, however, present insurmountable obstacles in component production and, consequently, GaAs technology will run its course.

In order to develop ….Read more

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