Non-Bauxite Sources of Alumina: A Survey of Canadian Potential
CIM Bulletin, Vol. 69, No. 774, 1976
N. W. Bliss, Alcan International (1975) Ltd., Montreal, Que.
Bauxite has been the almost universal ore of aluminum for about 100 years, with most of the world's reserves occurring in the developing countries. As a result of fiscal and political activities prompted in part by the energy crisis, the formation of the IBA combined with increasing freight and labour costs, these reserves are no longer as competitive or as secure as they once were. This has given fresh impetus to the development of processes for alumina production that utilize raw material other than bauxite. Canada has no bauxite and_ it is prudent to look for alternative raw materials within our own boundaries suitable for one of these processes.
Of the three igneous rocks that have been used as a source of alumina, only anorthosite is considered as a potential source in Canada. The Al content would be extracted by a sinter process, which currently requires a raw material with a minimum of 28% A120S. Thus, about U tons of anorthosite and 10 to 12 tons of limestone are needed to produce one ton of alumina. There are two petro-logically distinct types of anorthosite, one containing the plagioclase andesine-labradorite and around 26% Al,,O3 and the other containing upwards of 30% A12O3 in by-townite-anorthite; for our purposes they_ may be considered as low- and high-alumina anorthosite respectively. The high-alumina anorthosites are somewhat rare; the low-alumina anorthosites are much more common, particularly in Eastern Canada. Geologically speaking, there is no shortage of anorthosite in Canada. The reserves are immense, although their low A12O3 content coupled with considerations of location, access and proximity to limestone could be constraints to their development. Fly ash from coal-fired thermal power stations and nepheline syenite can also be used in a sinter process, but neither is likely to be utilized in Canada in the immediate future.
The H+ process utilizes an acid attack to leach Al from a raw material with at least 20% A1203. One of the best raw materials is kaolinite-bearing clay; not only is it high in Al, but most of it can be extracted. With the possible exception of the Whitemud clay in Saskatchewan, Canada is apparently deficient in clays with sufficient reserves to support an alumina plant utilizing the H+ process. Low-alumina clays with illite and montmorillonite may also prove to be a suitable raw material if advantageously sited with respect to industrial centers. The average shale contains only 15% Al^Os, much of which may be contained in minerals, such as feldspar, not amenable to acid leaching. If shale is used as a source of alumina, it will be because it contains some other valuable commodity, such as oil or uranium, the extraction of which leaves the spent shale upgraded in extractable A12OS and lowers the over-all costs to a point where it is economic. Thus, rejects from coal washing plants are -most commonly considered as a source of alumina; they are already mined, are available in large and ever increasing amounts, and may contain significant amounts of combustible material which upgrades the A1203 content of the resulting ash. Coal rejects from existing and developing coalfields in Alberta and British Columbia are a possible source of raw material, but present data indicate they may contain insufficient A12O3.
Alumina, Anorthosite, Nepheline syenite, Phonolite, Clays, Shales, Coal rejects, Fly ash.