Copper Ore Beneficiation Technology

Ores in which the main metal is copper are 90-95% processed by the flotation method and only 5-10% of ores are subject to metallurgical processing or other enrichment methods.

Flotation (French flottstion, from flotter - to float on the surface of water) is a method of enrichment based on the difference in the physical and chemical properties of the surface of materials, their ability to be wetted by water. Some minerals (hydrophobic) in a finely ground state in an aqueous medium are not wetted by water, stick to air bubbles introduced into the water and float with them to the surface, other minerals (hydrophilic) are wetted by water, do not stick to air bubbles and remain in the volume of the pulp.

Of the one hundred and seventy copper-containing minerals currently known, about seventeen are used on an industrial scale (Table 1). Almost all copper-containing ores, as well as polymetallic ones, contain iron sulfides (Table 2).

Table 1. Characteristics of the main copper materials

Table 2. Characteristics of the main iron sulfide minerals

For easily enriched ores with uniform dissemination of copper minerals, small-capacity factories usually use single-stage schemes that include grinding and classification operations, primary flotation, control flotation, and one to three cleaning operations.

In high-capacity factories, two-stage schemes have become widespread, according to which, after stage I grinding to a size of 45–60% of class –0.074 mm, coarse copper concentrate and pyrite-containing tailings are separated. Coarse copper concentrate is further ground to 85–95% of class –0.074 mm and sent to cleaning operations.

When processing ores with a high content of primary sludge and soluble salts, flotation should be carried out in two cycles - sand and sludge. Separate flotation creates the most favorable conditions for the flotation of large and small particles - sludge (product waste, making up its dust and fine parts, obtained as a sediment during the washing of any ore material), which usually increase the overall consumption of reagents , suppress the flotation of large particles, sticking to them, creating abundant and strong foam. The scheme with separate flotation is used, for example, at the Dzhezkazgan plant (Kazakhstan), at the Butte and Twin Buttes plants (USA).

Disseminated copper ores (porphyry copper, copper sandstones and vein ores) are characterized by low content of pyrite sulfur and copper (0.4–2.0%), depending on the pyrite content, can be processed to obtain only copper concentrate or copper and pyrite concentrates. In the first case, collective flotation is used, and in the second, collective-selective or direct selective.

According to their textural features, copper-containing ores are divided into massive, or solid, and disseminated. Solid ores are usually richer and are characterized by a high sulfur content, represented by pyrite, intergrown with copper and zinc sulfides. The ratio of copper, zinc, and sulfur, for example, in solid copper pyrite ore reaches 1:1:20 (25). Such solid ores are copper and copper-zinc ores of the Urals, which are classified as difficult-to-dress ores.

Disseminated ores are poorer in terms of non-ferrous metal content, which does not exceed 1–2% in ordinary ores and 0.4–1.0% in poor ores. Depending on the copper content in the processed ore, copper ores are conventionally divided into rich (more than 2% Cu), medium (0.8–2.0% Cu), poor (0.5–0.8% Cu) and off-balance (less than 0.3 % Cu). Rich sulphide ores containing 2–3% Cu, with a high sulfur content (35–42%) can sometimes be sent directly to smelting in shaft furnaces. However, in world practice, 80% of Cu is currently extracted from concentrates obtained during the enrichment of copper ores.

Copper sulphide minerals (haljelpyrite – CuFeS ₂ , chalcocite Cu ₂ S, covellite CuS, bornite Cu ₅ FeS ₄ ) are well floated by sulphhydryl collectors (solid crystalline substances have a characteristic odour, do not have foaming properties, which allows regulating their consumption within a wide range without disrupting the foaming process) based on divalent sulphur in a fairly wide pH range, since they have a high sorption capacity, which depends on the degree of oxidation of the sulphide surface and the copper content. According to flotation by xanthates (salts of xanthic acid ROC(=S)SH), copper minerals can be arranged in the following sequence: chalcopyrite < bornite < covellite < chalcocite.

Copper-porphyry ore deposits are the largest in terms of copper reserves. The largest copper processing plants with a capacity of up to 90 thousand tons of ore per day and more operate on their basis. Primary copper-porphyry ores mainly include molybdenite-chalcopyrite ores with a low content (2-5%) of pyrite. The main technological features of the enrichment of these ores are:

– single-stage grinding to a size of 60–65% of the –0.074 mm class before collective copper-molybdenum flotation;

– regrinding of rough concentrates to 85–90% of the –0.074 mm class to obtain rich copper concentrates;

– in collective flotation, a pH of 10–12 is maintained by feeding lime to suppress pyrite (although for molybdenite flotation the optimal pH value is 7.5–8.0).

The most common scheme for these ores is the one with additional grinding of the middlings and their processing in a separate cycle. Pyrite concentrate from such ores is usually not extracted (with the exception of the Chuquicamata plant, Chile). Copper-porphyry ores (pyrite, chalcopyrite, chalcocite) are processed at the Almalyk and Balkhash plants (Uzbekistan, Kazakhstan).

For copper ores with an average pyrite content, both bulk-selective and direct selective schemes are used. During enrichment using bulk-selective schemes, copper minerals and pyrite are separated from gangue minerals by coarse grinding (up to 45–50% of the –0.074 mm class), when it is possible to obtain tailings with a waste copper content. Then, according to the bulk-selective flotation scheme, after grinding to the above-mentioned size, bulk flotation of copper and iron sulfides is carried out at a pH of no higher than 7.5 (the concentration of free CaO does not exceed 20–50 g/m3). The resulting bulk copper-pyrite concentrate, after regrinding to 80–95% of the –0.074 mm class, is mixed with lime at a pH of 12.0–12.5 (400–500 g/m3 of free CaO) and cyanide to suppress pyrite and sent for copper flotation. Tailings from control copper flotation of disseminated ores, as a rule, contain no more than 30–35% S, and are therefore sent to pyrite flotation, which is carried out after removing excess alkalinity to pH 5–7.

Xanthates (salts of xanthic acid ROC(=S)SH, average consumption is usually 10–30 g/t) and dithiophosphates (10 g/t) are used as collectors of sulphide copper minerals. A combination of reagent-collectors is widely used. For example, in flotation of copper ores abroad, reagent Z-200 (isopropylethylthionocarbamate) is used, which is the most selective with respect to pyrite in combination with isopropyl or amyl xanthates. A combination of sulfhydryl collectors with apolar ones (machine oil, kerosene, etc.) is often used. In the CIS, butyl xanthate (C5H9OS2K) is most widely used, and is used in all copper factories.

The total share of xanthates used in US plants is ~60%, dithiophosphates – about 40%. Suppressors of gangue minerals are not usually used in flotation of copper disseminated ores. But if the pulp has an increased content of slimes, then liquid glass (up to 0.4 g/t) is added to the main copper flotation and to the copper concentrate re-cleaning. If oxidized copper minerals are present in the ore, then sodium sulfide (200–300 g/t) is fed to the grinding and main copper flotation.

The requirements that copper and pyrite concentrates must meet are presented in Tables 3 and 4.

Table 3. Requirements for the quality of copper concentrate (according to OST 48-77-82)

Table 4. Technical requirements for pyrite concentrates obtained during flotation of sulphide ores (according to GOST 444-51 "Pyrite flotation")

Requirements for the obtained copper and pyrite concentrates are determined depending on the type of ore and the adopted method of their metallurgical processing.