Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2002-08-08
2003-12-02
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S050000
Reexamination Certificate
active
06656247
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the efficient and selective precipitation of manganese, from magnesium-containing solutions. More particularly, the invention relates to the removal of manganese from, for example, laterite ore waste solutions which are substantially barren of one or more of cobalt, nickel, copper and zinc, but which contain magnesium, manganese and aluminum.
BACKGROUND OF THE INVENTION
Mining and milling operations generate various types of toxic, metal containing effluents which require treatment prior to discharge to the environment. These effluents include, for example, acid mine drainage, mill tailings excess decant water, seepages, and acidic process waste streams. The most common of these is acid mine drainage, characterized by acidity (sulphuric) and metals, which may include aluminum, cadmium, chromium, cobalt, copper, iron, lead, magnesium, manganese, nickel, zinc and others.
The processing of nickeliferous lateritic ores by sulphuric acid leaching has gained considerable interest in recent years, with three commercial plants based on high temperature acid leaching coming on stream in Western Australia in the late 1990s. A number of similar operations are at various stages of development, throughout the world. The process generates acidic product liquors, containing nickel and cobalt, as well as most of the afore mentioned metals, as impurities. In addition, the product liquors contain significantly higher concentrations of manganese and magnesium, particularly relative to their concentrations usually encountered in acid mine drainage.
Various methods are used and have been proposed for recovery of the nickel and cobalt from such leach liquors. These fall into three general categories, including precipitation as sulphides, precipitation as hydroxides (to produce intermediates for subsequent refining) and direct solvent extraction. Most of these options require removal of at least some of the metal impurities prior to recovery of the nickel and cobalt. Recovery of the latter by sulphide precipitation requires prior neutralization of the acid but, because sulphide precipitation is relatively selective for the base metals, may require little or no prior removal of metal impurities. Recovery by the other alternatives also requires prior neutralization of the acid and removal and/or reduction of some of the metal impurities, such as aluminum, chromium and iron before recovery of the nickel and cobalt. Regardless of the method of recovery of the valuable metals, the barren or waste solution will still contain varying and variable concentrations of toxic impurities. In addition, some of the recovery alternatives for the nickel and cobalt may involve a co-extraction or co-precipitation of some of the metal impurities, which are removed or rejected at a later stage in the process, as a secondary waste or effluent stream which, in most instances, is recombined with the major effluent stream.
The most common and effective way of dealing with acidic metal containing effluents prior to discharge of the treated water to the local waterways is neutralization of the acid and precipitation of the dissolved metals as hydroxides, using suitable alkaline reagents. Lime is most commonly used as the neutralizing/precipitating reagent, because of its high reactivity, availability, and relatively low cost. Alternatively, the sequential use of limestone, to pH 5 to 6, in a first stage, to precipitate the bulk of the aluminum, chromium and iron, followed by lime, to pH 8 to 10, to precipitate the remaining metals, may be preferred. Depending on the environmental regulations, which are usually site-specific and may vary considerably from site to site, the treatment with the combination of limestone and lime, or by lime alone, may be adequate for meeting the requirements for the treated water. Air is frequently used during the neutralization, to oxidize ferrous iron to ferric and, when using limestone in the first stage of neutralization, to remove the generated carbon dioxide prior to the addition of lime.
A treatment to a pH range of 7 to 8 is generally sufficient for removal of most of the impurities to acceptable levels. One exception, however, is manganese. According to one reference (N. Kuyucak, “Conventional and New Methods for Treating Acid Mine Drainage,” proceedings of CAMI '95 Conference, Oct. 22 to 25, 1995, Montreal, Quebec), removal of the manganese requires strong oxidation followed by liming at pH greater than 10. Many of the effluents also contain appreciable concentrations of magnesium, however, and neutralization to such high pH levels also results in precipitation of the magnesium, which is generally not categorized as toxic nor whose removal is required. For example, McLaughlin et al, in a paper entitled “A Comparison of Selected Acid Mine Drainage Treatment Processes” (Preprint 96-145, SME Annual Meeting, Phoenix, Ariz., March 11 to 14, 1996) state that to remove manganese to low levels in a reasonable period of time (pH approximately 10.5), a significant portion of the magnesium present will also precipitate. This is further illustrated in a paper by Feng et al, entitled “Treatment of Acid Mine Water by Use of Heavy Metal Precipitation and Ion Exchange” (Minerals Engineering, Vol. 15, No. 6, pp. 623 to 642, 2000). In their work, acid mine water, containing a wide range of metals, including 113 ppm Mn and 359 ppm Mg, was treated with lime to precipitate the metals. By pH 9.1, the Mn had been precipitated to 15.7 ppm, without appreciable co-precipitation of Mg. Further liming, to pH 10.1 had lowered the Mn concentration to 2.6 ppm, but with co-precipitation of about 60% of the Mg, to 143 ppm. By the time the Mn had been removed to 1.1 ppm, the co-precipitation of the Mg had been even more complete, to 0.5 ppm. Thus, additional reagent had to be added to precipitate the Mg with the Mn to get the Mn concentration to the required levels. In instances where removal of magnesium is not required and/or where more effective and selective removal of the Mn is required, the alternative treatments which have been adopted have included the use of strong chemical oxidants or the use of sulphiding reagents.
Laterite ore leach solutions and the resultant waste solutions, after recovery of the nickel and cobalt, are characterized by high concentrations of most impurity metals-relative to typical concentrations in most acid mine waters and other mining and milling wastes. For example, the barren solutions may contain from 0.5 to 5 g/L Mn, and from 3 to 50 g/L Mg, depending on the ore type treated, and the extent of solution recycling within the processing plant. Environmental regulations for plant effluents vary considerably, depending on the nature of the receiving waters, location and a number of other factors. In many locations, the discharge of magnesium containing solutions is allowed, whereas prior removal of manganese to trace levels is required. The allowable manganese level may range from several tens of mg/l, to 1 mg/l or less, depending on the site. Although, as noted earlier, the selective removal of manganese might be accomplished by the use of strong oxidants or of sulphiding reagents, the relatively high concentrations and quantities of manganese in laterite leach effluents would tend to make these alternatives economically unattractive or prohibitive. The ability to effect an extensive and selective removal of the manganese, to trace levels, in the presence of appreciable concentrations of magnesium with inexpensive reagents such as lime would, therefore, be highly desirable.
SUMMARY OF THE INVENTION
The present invention provides a process for selective removal of manganese from acidic waste solutions which are preferably substantially barren of one or more of cobalt, nickel, copper and zinc, but which contain manganese, magnesium and aluminum (and possibly other metals, such as iron and chromium), without unnecessary co-precipitation of magnesium. The process not only enables the use of inexpensive reagents, such as lime, it al
Genik-Sas-Berezowsky Roman Michael
Stiksma John
Andrews Melvyn
Dynatec Corporation
Greenlee Winner and Sullivan P.C.
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