Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Iron group metal
Reexamination Certificate
2000-04-07
2002-06-25
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Iron group metal
C423S147000, C423S050000
Reexamination Certificate
active
06409979
ABSTRACT:
The present invention relates to a method for precipitating nickel and cobalt from acidic aqueous solutions. The method is suitable for use in the recovery of nickel and cobalt from ores or concentrates, especially lateritic ores and concentrates obtained from lateritic ores.
Lateritic ores are commonly treated to recover nickel and cobalt therefrom by pressure leaching with an acid. This results in the extraction of nickel and cobalt from the ore into the aqueous phase. The leaching step also results in the extraction of other metals in the ore into the aqueous phase. Typically, manganese, magnesium and iron are also leached from the ore and a mixed solution containing several metal ions is produced.
Typical nickel-ore processing plants treat the leach solution to produce a precipitate containing nickel and cobalt and further treat the precipitate to separately recover nickel and cobalt at a satisfactory purity. The further treatment of the precipitate may involve a further leaching to extract nickel and cobalt, followed by liquid-liquid extraction to separate the nickel and cobalt and recovery stages to separately recover nickel and cobalt.
Operating experience with plants that treat nickel ores has shown that a number of difficulties exist in the treatment of the aqueous phase resulting from the pressure acid leaching of the ore. For example, adding sodium hydroxide or sodium carbonate to the acidic leach solution results in a very fine or slimy precipitate being formed which is difficult to settle and filter. Filter cake washing can also be difficult due to the small particle size of the precipitate. Precipitation with calcium hydroxide results in the formation of an insoluble calcium sulphate precipitate, resulting in contamination of the nickel/cobalt product. Precipitation of nickel and cobalt as a sulphide is selective and gives a precipitate that is readily filterable. However, the equipment required to carry out the precipitation is capital intensive, as is the equipment required to produce the hydrogen sulphide. The resultant nickel cobalt sulphide requires pressure leaching to dissolve, which also requires high cost equipment. The sulphate that results requires eliminating either as ammonium sulphate or sodium sulphate. This requires ammonia or sodium hydroxide to be used as the neutralising agent, both of which are expensive.
Another method of precipitating nickel and cobalt from leach solutions is to add magnesium oxide to the acidic leach solutions. Precipitation with magnesium oxide should result in the dissolution of magnesium to form soluble magnesium sulphate. However, this is frequently an imperfect operation which results in a nickel/cobalt product containing high levels of magnesium.
All of the above techniques apart from sulphide precipitation also lack selectivity with respect to manganese precipitation, resulting in a nickel/cobalt precipitate high in manganese.
An earlier patent recognising some of the above difficulties is Australian Patent No. 655774 (AU-B-22766/92) in the name of Hoefer. This patent discusses the treatment of a liquor from a leaching or beneficiation circuit for oxidised nickel-containing ore by precipitating the valuable species and to pass the liquor through a thickener/filtration circuit to separate the valuable species from the liquor. The patent states that this is not a satisfactory solution for nickel because the nickel precipitates that can form most readily, such as nickel hydroxides and sulphides, are gelatinous and difficult to thicken and filter. In particular, the nickel precipitates tend to blind filters quickly. The patent addresses the problems of thickening and filtering by adding an inert particulate carrier and a flocculant to the liquor to form flocs. However, this process requires the addition of further materials to the liquor and does not address the issue of manganese precipitation.
U.S. Pat. No. 2,899,300 in the name of Bailey (assigned to Quebec Metallurgical Industries Ltd) discloses a process for treating nickel lateritic ores. The process incudes contacting the ore with sulphuric acid in an amount sufficient to saturate the ore. The acid-saturated ore is dried by baking at a temperature between 100-150° C. and subsequently crushed. The crushed ore is then leached with water to obtain a leach solution containing nickel and cobalt values, as well as iron, manganese and chromium. The pH of this leach solution is then adjusted to within the range of 3.5-4.2 to precipitate ferric iron. After removing the iron-containing precipitate, reactive magnesia (either in powder or milk form) is added to the solution to bring its pH up to about 8.2 to thereby precipitate a nickel-containing concentrate. Practically all of the nickel and cobalt is precipitated from solution, along with the remaining iron and about 50% of the manganese. The precipitate is stated to settle rapidly to a dense pulp.
The example included in this patent treats a lateritic ore having a low manganese content of 0.26 wt % Mn. The leach liquor has a ratio of (nickel plus cobalt) to manganese in the leach liquor of 11.2. The same ratio in the final precipitate is 17.9, showing that only a relatively small concentration of nickel and cobalt relative to manganese, is achieved. In other words, the precipitation is not selective to nickel and cobalt precipitation. Accordingly, the process described in U.S. Pat. No. 2,899,300 would be only suitable for treatment of lateritic ores having low manganese contents.
Furthermore, the precipitated product contains significant quantities of iron (6.2 wt %). This can be deleterious because the presence of iron in the precipitate can suppress re-leaching of nickel and cobalt from the precipitate.
U.S. Pat. No. 3,466,144 in the name of Kay (assigned to American Metal Climax, Inc.) describes a hydrometallurgical process for recovering nickel and cobalt from nickeliferous oxidic ores. In the process, the ore is leached with sulphuric acid at elevated temperature and pressure. The loaded solution is separated from the solid residue. The pH of the loaded solution is increased to about 3.4-4.5 by adding lime or magnesia to precipitate iron, aluminium and silicon whilst the nickel, cobalt and manganese remain in solution. The resulting precipitate is separated from the solution.
The loaded solution is then treated by adding magnesia until the pH is at least 8 in order to precipitate the nickel, cobalt and manganese. The thus-formed hydroxides of nickel, cobalt and manganese are then separated from the solution (e.g. by vacuum filtration) and the filter cake is washed with water and sent for further refining.
U.S. Pat. No. 3,466,144 discloses a two-stage precipitation in which iron is first removed from solution, followed by a non-selective precipitation of nickel, cobalt and manganese from solution. This results in a solid precipitate that contains significant quantities of manganese.
U.S. Pat. No. 3,720,749 in the name of Taylor et. al. (also assigned to American Metal Climax, Inc.) discloses a process similar to that described in U.S. Pat. No. 3,466,144 but with the improvement that the first stage precipitation to remove impurities such as dissolved iron, aluminium and silicon from the solution is conducted by adjusting the pH at elevated temperature and pressure. This enables a wider pH range to be used for the first stage precipitation. The second stage precipitation to precipitate nickel, cobalt and manganese from solution may be conducted by adding a neutralising agent to cause precipitation of hydroxides or by adding H
2
S to cause precipitation of sulphides. Example 2 shows the stage 2 precipitation being conducted by adding MgO until the pH of the leach solution falls within the range of 5.6 to 8.8. This resulted in precipitation of 88.4% of the nickel, 83.7% of the cobalt, 57.8% of the manganese and 30.6% of the chromium. Clearly, the process does not provide for selective precipitation of nickel and cobalt over manganese.
The present invention provides a method for precipitating nickel and cobalt that overc
Bos Steven
Centaur Nickel Pty Limited
Christensen O'Connor Johnson & Kindness PLLC
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