Today, exportable refractory-grade bauxite (essentially all diasporitic) is mined mainly from two provinces in China-Shanxi and Guizhou. Shanxi reportedly exports two-thirds of the total.
The Guizhou and Shanxi materials have similar characteristics, however, Guizhou has the disadvantage of higher TiO2 (3.7% typical vs. 4.2) and alkalies (0.2% typical vs. 0.6).
Although there have been unconfirmed reports of higher bulk densities in Guizhou, the two provinces are essentially the same in principle, with Shanxi possibly having the edge. In this case, chemistry is a minor influencing factor (lower alkali content, higher Al2O3 in Southern Shanxi), meaning bulk densities in China are primarily a function of the calcining equipment and process.
With residence time as a primary factor, their minimum control rudimentary shaft kilns are limited to maximum range BSGs (3.20-3.25). Rotary kilns can produce up to the 3.30 range and the Chinese round kilns can produce up to 3.35 by means of a special 18th century burning procedure.
It is estimated that 50% of Chinese refractory-grade bauxite is produced in updraft shaft kilns, with the remainder split between round and rotary.
The Chinese bauxite supply picture is complicated because there are ~300 bauxite mines in China, with the exported product rarely representing a single mine source. When ISO-9000 comes to refractory-grade bauxite in China, it will be with some difficulty.
The supply of Chinese refractory-grade bauxite has improved during the past 20 years-in part due to the installation of several controlled processing plants in Tianjin. However, the basic supply from the mine to the kiln to the port still involves considerable rudimentary control and consequent quality variations. This could improve significantly if experienced third parties get involved in the mining and calcining of the material.
Despite numerous complaints that the Chinese producers have been dumping, it does not appear to be probable. In any case, recent export and provincial taxes will now force the Chinese prices somewhat closer to world market levels. This will tend to promote a switch back to South American bauxites.
Refractory-grade bauxite also is used to produce brown-fused alumina, a significant product in China. Total current production there is reportedly in excess of 300,000 tpy.
The MSL Minerais (CAEMI) operation is the new supplier on the block. Despite some apparent built-in disadvantages, it has managed to develop a niche market and justify the installation of a second rotary kiln in 1994. Thus, increasing total productive capacity to ~140,000 tpy.
Although the bauxite vein at CAEMI is only 1-3 m thick, the relatively 8-12 m thick overburden is within an acceptable proportion. Therefore, mining costs should be relatively low. The crude ore must be beneficiated, first by crushing (10 mm maximum) washing and screening, then with a heavy media process to remove iron. After calcining, the material goes through eight iron-removing magnetic separators. Despite the relatively high SiO2 content (approaching 10%), the beneficiation costs and relatively higher fuel costs for calcining, the finished product is priced lower than Guyana RASC, and has gained significant market share-particularly in Europe.
The higher SiO2 and lower alkalies in the MSL bauxite, together with a uniform fine kiln feed size, contributes to the higher level of mullite (and lower corundum) in the final product. TiO2 is a low 2.2%, tielite a low 0-2%.
Bauxite was first identified in Guyana in the period 1897-1910. Although Alcoa Industrial Chemicals began alumina-grade bauxite production in Guyana in 1917, and Alcan took over in 1929, it was not until 1938 that refractory-grade bauxite was separately identified and produced. The typical processing of Guyanese bauxite is straightforward: Bauxite is crushed to -9 cm, washed and screened, crushed to -4 cm, rewashed, then rotary kiln calcined, with some final de-ironing before shipment.
Refractory-grade bauxite from Guyana presently falls into two separate geographic sourcings: the original Linmines’ home of the traditional world standard RASC bauxite; and the Berbice/Bermine operation, the latter primarily a source of abrasive- and chemical-grade bauxite.
Reserves at Linmines are substantial. Ongoing improvements to operating practices and costs began five years ago, with the consequent gradual improvement to a global competitive marketing position.
A privatization program now in progress in Guyana should contribute to an improved bauxite product, availability and costs.