Blog of Mineral Processing (Metallurgy) Articles

In the case of pellets it was observed that incremental additions of olivine to any of a series of pellet concentrates invariably caused the pellets to become progressively more ferromagnetic after induration. At first, it was assumed that what little magnesioferrite formed in such pellets stabilized magnetite, a comparable spinel structure, in solid solution. However a systematic study showed that near quantitative yields of virtually pure magnesioferrite were produced during induration of green pellets containing up to 4 percent of fine olivine. The gangue content and mineral natures of the pellet concentrates had little to do with the formation of this magnesioferrite phase.

The quantitative repartitioning of magnesia, a strong base silica to the ferric oxide phase was quite unexpected. One would not expect a base like magnesia to partition from a strong acid to a weak acid. Furthermore, when it was recognized that 1 part by weight of MgO or 2.25 parts of olivine would produce 5.0 parts by weight of magnesioferrite (MgFe2O4), this spinel phase became the obvious source of the ferromagnetic properties. When one considers that magnesioferrite has a density well below that of hematite, the principal phase of an indurated pellet, it becomes clear that as much ….Read more

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

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

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%.

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

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

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