METHOD FOR SELECTIVE FLOTATION OF COPPER

FIELD OF THE INVENTION

The invention relates to a method whereby the pH buffer capacity of the feed that is routed to selective copper flotation is raised. The rise in pH buffer capacity is accomplished by feeding a soluble basic mineral among the ore in the pretreatment stage. The pH buffer capacity means the sensitivity to change and the reversal capacity of the pH of the feed as acid or alkaline chemicals are added.

BACKGROUND OF THE INVENTION

Attempts have been made to find various methods to exploit fine complex sulphide ores, whereby different valuable minerals could be recovered selectively. A complex copper sulphide ore for instance may contain zinc, lead, nickel and iron as separate sulphides. Selective separation of copper sulphide concentrate by flotation from these kinds of feed types can be done in several different ways.

The selective flotation of copper from a copper-lead-zinc sulphide ore is described in US patent application 5,439,115. Pre-aeration of the ore slurry is typical of the method in order to achieve the desired oxidation-reduction potential range. After this the slurry is conditioned, it is aerated to exactly the desired potential of 60 - 340 mV and to a pH value of 8.5 - 10.0 by means of slaked lime (Ca(OH) ₂ ), and subsequently the selective flotation separation of copper is performed. Xanthate is used as the collector. After copper flotation the pH of the slurry is raised to a value of 9.3 - 12 with slaked lime to froth the lead. The large consumption of lime and weak selectivity can be considered to be the disadvantages of this method, particularly in the treatment of partially oxidized ores.

Another selective flotation method for copper from a copper-lead-zinc sulphide ore is described in US patent publication 5,074,994, in which the ore slurry is conditioned by means of bisulphite and causticized starch at a

pH of 5.7 - 6.5. The conditioning chemicals also function as zinc and lead depressants. After conditioning, selective flotation of copper is performed using a combination of dithiophosphates and dithiophosphinates.

One known group of valuable metal sulphide collectors are thionocarbamate compounds, which are selective in relation to for example pyrite and pyrrhotite. In this connection valuable metal sulphides refer to copper, zinc and lead-nickel sulphides. Use of thionocarbamate compounds as a collector in the flotation of sulphide minerals is described for instance in US patent publication 4,584,097. The concentrate obtained is a bulk concentrate of copper, lead and zinc.

When the material for treatment contains several sulphides i.e. a complex sulphide ore, where one wishes to use a thionocarbamate compound as collector and to form copper sulphide concentrate, that does not include significant amounts of zinc or lead, suitable depressant chemicals should be used in this regard. Known lead and zinc sulphide depressants include various sulphur oxocompounds such as metabisulphite (MBS) and dithionite as well as various organic depressant chemicals such as dextrin compounds. The method works well at electrochemical potential ranges typical of copper minerals, but the drawback is that sharp copper flotation only takes place in quite a narrow pH range, typically 6.5 - 7.0, preferably 6.7 - 6.9, whereupon the selectivity with regard to lead sulphides and zinc sulphides is best. To guarantee sufficient flotation time, maintenance of selectivity requires the dosing of sulphur oxocompounds functioning as depressant chemicals at several points in the flotation circuit. This in turn leads to variation in pH level and thus to non-selectivity without multi-stage pH measurement and control for feeds that possess a low pH buffer capacity.

PURPOSE OF THE INVENTION

The purpose of the present invention is to eliminate the shortcomings of the methods according to the prior art described above. According to this method a copper concentrate is formed from a complex fine-ground sulphide ore by

means of selective flotation by raising the buffer capacity of the ore feed entering flotation, whereupon flotation can be performed without multi-stage pH measurement and control.

SUMMARY OF THE INVENTION

The essential features of the invention will be made apparent in the attached claims.

The invention relates to a method whereby the pH buffer capacity of the feed to be routed to selective copper flotation is raised. The copper sulphide concentrate is formed by performing the necessary pretreatment on a complex sulphide ore, after which the fine-ground ore is fed to separation flotation. In flotation, a copper collector chemical and lead sulphide, zinc sulphide, nickel sulphide and iron sulphide depressant chemicals are used. The increase in the pH buffer capacity of the complex sulphide ore takes place by feeding a soluble basic mineral with the ore in the pretreatment stage.

The basic mineral is preferably limestone or dolomite. The basic mineral is added preferably to the crushing, grinding or conditioning stage of pretreatment, typically as chunks, chippings, powder or slurry. The amount of mineral to be fed is in the range of 0.05 - 5% of the amount of feed.

The copper collector chemical used is preferably a thionocarbamate compound and the lead sulphide, zinc sulphide, nickel sulphide and iron sulphide depressant chemical some sulphur oxocompound such as metabisulphite or dithionite. In addition to oxocompounds, other depressant chemicals may be used, for instance organic depressants such as dextrin.

DETAILED DESCRIPTION OF THE INVENTION

The utilization of pure sulphide ores is generally relatively straightforward, but since they are limited in quantity, it is becoming more common to study and utilize complex fine sulphide ores. A complex ore here means that it

contains several valuable minerals, such as for example copper sulphide, zinc, lead and nickel sulphide as well as iron sulphides such as pyrite and magnetic pyrite. The pH buffer capacity of such kinds of complex ores is typically low.

Obviously, the necessary pretreatment is performed on the ore that is going to flotation, such as crushing, grinding and conditioning. It is also preferred that the electrochemical potential of the slurry entering copper separation flotation is adjusted to the best zone for copper minerals before flotation. Typically this is done by means of aeration.

One practicable method for fabricating a selective copper flotation concentrate from a complex sulphide ore is described in the prior art, in which a thionocarbamate compound is used as the collector chemical and some oxocompound of sulphur is used as depressant chemical, such as metabisulphite (MBS) or dithionite and if necessary other depressants, for example organic depressant chemicals such as dextrin. As stated above, the drawback of the method is considered to be the relatively narrow pH zone it requires to maintain selectivity in a flotation circuit with sufficient retention time, resulting in the need for multi-stage pH measurement and pH control for feeds with a low buffer capacity. The pH buffer capacity of typical complex ores is low, because they do not generally contain basic gangue minerals.

Now a method has been developed, in accordance with which the pH buffer capacity of a complex sulphide ore can be regulated by adding a soluble basic mineral to the feed entering flotation. The amount of mineral required depends on the dosage requirement of the acidic depressant chemical, but typically it is 0.05 - 5% of the amount of the feed. The quality of the mineral is not a critical factor as long as it is sufficiently homogenous. The basic mineral is typically limestone, CaCO3. Another suitable mineral is for example dolomite, CaMg(CO ₃ ) ₂ and other basic minerals can also be used, such as various serpentinite minerals.

Control of the pH buffer capacity enables the dosing of depressant chemicals without harmful pH fluctuations, because as it dissolves, the basic mineral balances out the pH value of the slurry, thus placing it in the target zone. When a basic mineral is used for pH control, the pH of the slurry does not rise too high, which is a risk if some other chemical is used exclusively for pH control, such as dehydrated or slaked lime (CaO or Ca(OH) ₂ ).

The basic mineral is preferably added for example as chunks or chippings into the ore crushing or grinding stage, or as fine powder or slurry into the conditioning stage. When added to the grinding feed, the mineral prevents the electrochemical potential of the slurry from falling to too reducing for instance during iron bar or iron ball milling. In this way the mineral improves the operational requirements for selective copper flotation and diminishes the need for aeration in separation of the copper mineral in order to achieve the necessary electrochemical potential level.