Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2000-11-29
2002-05-21
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S150300, C423S145000
Reexamination Certificate
active
06391089
ABSTRACT:
FIELD OF THE INVENTION
The invention describes improvements in the commercial-scale processing of nickel and cobalt containing laterite ores for the recovery of these metals, by reacting such ores with sulphuric acid at elevated temperatures and pressures
BACKGROUND OF THE INVENTION
For over a century, nickel laterite ores high in magnesia, relatively low in iron, and enriched in nickel, commonly referred to as garnierite ores or saprolite ores, have been processed by pyrometallurgical means to produce either a ferronickel, a Class II nickel product that could go directly to market for the production of stainless steels, or to produce an intermediate sulphide “matte” product that could go to refineries for conversion to either Class I or Class II nickel products. A good portion of the cobalt would be lost, some in the slag during the smelting stage, and in the case of ferronickel most of the cobalt would be present as a product impurity of no value. Such pyrometallurgical processes involve drying the humid ores, preheating them with or without effecting a partial reduction, and subsequent reduction smelting at high temperatures in electric furnaces. It is axiomatic that such pyrometallurgical processes consume high amounts of energy per unit of nickel production, and in most cases result in complete loss of value of the cobalt that accompanied the nickel in the ore.
About half a century ago, an ammoniacal leaching process was developed and commercialized which could treat laterite ore relatively high in iron and of lower nickel content than the garnierites and saprolites. It employed a combination of pyrometallurgical and hydrometallurgical technologies. The laterite ore is first dried and then subjected to partial reduction in Herreschoff furnaces or rotary kilns, at elevated temperatures but well below smelting temperatures, to selectively reduce the nickel and cobalt but only partially reduce the iron. This partially reduced calcine is then quenched and leached in ammoniacal carbonate solutions to dissolve nickel and cobalt; and the nickel is subsequently recovered from the ammoniacal leach solution as a nickel hydroxide/carbonate which would then be converted to a Class II nickel oxide or to utility-grade nickel. In some cases the nickel solutions would proceed to electrolytic refining for the production of refined nickel. Nickel extractions seldom exceed 80% and cobalt extractions seldom exceed 45%. While this hybrid pyrometallurgical-hydrometallurgical process could treat the high-iron, low-magnesia and low-nickel laterite ores, often referred to as limonite ores, and is less demanding of energy than the smelting process, in actual continuous practice, the nickel recoveries often fall below 75% and cobalt recoveries below 40%.
Research in the early 1950's demonstrated that by subjecting the high-iron, low-magnesium and low-nickel laterite ores, that is the limonites, also containing significant quantities of cobalt, directly in their humid state to sulphuric acid at elevated temperatures and pressures, that nickel and cobalt extractions of over 90% could be achieved with the energy requirement only a fraction of that required by the smelting or ammoniacal leaching processes. While this technology heralded a new era for the production of nickel and cobalt, only one commercial plant was built at Moa Bay in Cuba. This plant confined itself to the processing of limonites very low in magnesia content, i.e., with less than 1% magnesium oxide, and operated at around 240° C. and 475 psig. The plant which is in operation today, employs pachuca-type autoclaves which rely on the process steam to provide both the heat requirement and the agitation which is inadequate and promotes build-up inside these autoclaves which in turn necessitates frequent shutdowns for cleanouts. The product of the Moa Bay plant is an intermediate nickel-cobalt sulphide, which is sent overseas for refining to marketable nickel and cobalt end products.
The value of this new hydrometallurgical technology that could treat humid ores directly without drying and which yields impressively high extractions of nickel and cobalt, became more and more appreciated as a result of the energy crises of the 1970's and 1980's and as a need grew for new sources for cobalt outside of Zaire and Zambia whose production had dropped off drastically. At the same time, the development and demonstrated success of large-scale mechanically-agitated compartmentalized autoclaves in other industries such as the gold industry, gave added interest for application of such reactors to the processing of nickel-cobalt laterites. In such reactors, the requirement for process steam and for agitation are managed and adjusted independently one of the other. Furthermore, extensive research developmental work carried out by P. C. Duyvesteyn, G. R, Wicker, R. E. Doane of Amax Extractive & Development Inc. “An Omnivorous Process for Laterite Deposits”, International Laterite Symposium, Evans, Shoemaker, Veltman Eds., TMS-AIME, Kingsport Press, Kingsport Tenn., 1979, demonstrated that enhanced results could be realized at somewhat higher temperatures of around 270° C. and corresponding pressures of around 800 psia; and that this new technology employing mechanically-agitated reactors need not limit itself to the very low-magnesia laterite ores, but could be applied to ores containing several percent of magnesia. Of course, acid requirements increase significantly as the magnesia increases as does the requirements for neutralizing agents. The greatest impetus to proceed with this new technology comes from engineering and economic analyses which indicate that hydrometallurgical process plants could be constructed at a capital cost per unit of annual nickel and cobalt production substantially below that of the established conventional processes and would yield a unit cost of production which permits economic treatment of limonites with as little as 1% of nickel, material that up until now had been considered as overburden and uneconomical to process, i.e., material that previously could not be classified as ore. This has led to the construction of three separate acid pressure leaching plants in Australia, with commissioning in 1999/2000.
U.S. Pat. No. 4,541,994, 1985, assigned to Lowenhaupt et al. speaks of reacting “coarse, magnesium rich fractions” with partially neutralized pregnant liquors produced by high pressure leaching, at lower pressures, and claims carrying out of such reactions “at a pressure of from atmospheric to about 300 psig”, also “wherein said pressure is atmospheric and said temperature is below 80° C.”, also “wherein said temperature is about 60° C.”, and also “wherein said temperature is ambient”. Their atmospheric leach tests Nos. 7, 8, 9 and 10 at 80° C., for example, demonstrated that nickel and cobalt tend to be upgraded in the fine fractions and magnesium in the coarse fractions. In these tests, the Mg:Ni ratio in the +200 mesh size in relation to the Mg:Ni ratio in the −200 mesh averaged 2:1; and the Mg:Co ratio in the +200 mesh size in relation to the Mg:Co ratio in the −200 mesh size averaged 2.1:1. Only the −200 mesh size would proceed to acid pressure leaching. While less acid would thus be required per unit of nickel and cobalt to yield high extractions in the pressure leach, overall nickel and cobalt recoveries would be greatly decreased.
Currently, in preparation for the pressure leaching, the humid predominantly limonitic laterite ores are pulped with substantial quantities of calcium-free water either from a “fresh” water source or with de-ionized saline water, to a pulp density usually under about 40% solids; and excess acid is added to the autoclaves to effect the desired leaching in 60 minutes or less, when employing reaction temperatures of up to 270° C.
It is well understood and appreciated by those familiar with acid pressure leaching of laterite ores, that the pH of acidic leaching solutions is different at elevated temperatures than at temperatures below 100° C.; and
Andrews Melvyn
Hill & Schumacher
Schumacher Lynn C.
LandOfFree
Acid leaching of nickel laterite ores for the extraction of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acid leaching of nickel laterite ores for the extraction of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acid leaching of nickel laterite ores for the extraction of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2870892