Copper and Copper-Gold Ores

Most copper ores today are mined from porphyry deposits, though a few vein-type deposits are still being exploited. Nevertheless, the choice of reagent suite for flotation of these ores depends more on the type and amount of the various minerals present, than on the origin of the ore. The major considerations in processing copper ores in general include:

• The ratio of chalcopyrite to secondary copper minerals such as chalcocite, covellite, bornite, etc.
• The amount and activity (tendency to float) of the iron sulfide minerals such as pyrite, marcasite, and pyrrhotite. 
• To what extent, if any, the copper minerals are tarnished or oxidized . 
• The presence of minerals containing penalty elements such as lead, zinc, arsenic, antimony and bismuth .
• Whether or not the ore contains a significant amount of primary slimes such as clays  and other talcose minerals .
• The degree of liberation of the various valuable and gangue minerals.
• The natural pH of the ore pulp after grinding.
• Whether or not the ore contains recoverable amounts of gold and silver and how these are associated with the other minerals. 

Role of pH and pH Modifiers

The use of a lime is practically universal in the flotation of copper ores. Lime  alkalinity  is generally maintained in the pH range of 9.5 to 11.0 in the rougher circuit and as high as 12.0 in the cleaner circuits. The higher pH serves to depress the iron sulfide gangue minerals, which are commonly present. The pH can also influence the froth structure and floatability of the copper minerals. 
These characteristics are adversely affected below some minimum pH value, which varies from ore to ore, especially when the less selective collectors such as xanthates and dithiophosphates are used. If free metallic gold is present, the use of lime should be carefully controlled, since excessive lime concentrations may have a depressing effect on the gold. If lime depression of gold becomes a problem, soda ash can be used in place of lime. In a limited number of operations, flotation is carried out at natural pH without any pH regulating agents, or in acid circuits.

Choosing a Reagent Scheme

The choice of collectors can be made on the basis of the mineralogy of current and new/future ores, metallurgical objectives, and the operating conditions. In existing plants, the choice of collectors is influenced by the pH of the operating circuit and whether or not the pH can be changed. For new ore bodies, a thorough investigation of representative chemical families, selected on the basis of ore characteristics, will be required (see Statistical  Methods in Mineral Processing). Best metallurgy is usually obtained by taking advantage of the unique chemistries of Syensqo's proprietary products. Plant experience from Syensqo's many years as mining chemical leaders has established that our Flotation Matrix™ 100 (FM-100)  formulated products offer a wide range of benefits as is discussed later in this section.

After the initial selection of collector is made on the basis of the factors mentioned above, it is necessary for plant metallurgists to work with Syensqo on collector optimization in the plant in order to find operational or chemical conditions (dosage, addition point, air flow rates, cell levels, etc.) that provide optimum metallurgy with respect to the dynamic metallurgical and economic objectives. In some cases, slight modification of the selected collector/formulation may be required with the ultimate goal of providing a robust reagent that is suited for various ore types treated in the plant.
 

Some of the challenges faced in processing copper ores include any combination of the following:

• Achieving selectivity against main sulfide gangue minerals such as pyrite and pyrrhotite and, to a lesser extent, unactivated sphalerite and galena if present. Fine dissemination of copper sulfides in massive iron sulfide hosts and the concomitant intimate mineral associations requires very fine grinding for adequate liberation of the copper minerals. The presence of secondary copper and/or oxide copper  minerals can also lead to inadvertent activation of pyrite and sphalerite, making the separation more challenging and requiring high lime dosages. 
• Achieving selectivity against arsenic and antimony minerals such as tennantite, tetrahedrite, enargite, realgar, orpiment, proustite, and pyrargyrite .
• Issues related to pulp rheology or froth stability/instability due to the presence of problematic non-sulfide gangue minerals such as clays, Mg silicates, “slimes” including: chlorite, bentonite, kaolin, serpentines, tremolite. These can impact flotation kinetics of value minerals and promote loss of the same to tails.
• Issues related to the presence of carbonates such as calcite/aragonite, dolomite and/or magnesite,  e.g. the impact of calcium and magnesium ions on pulp and froth behavior as well as on mineral flotation kinetics and even reagent performance.
• A more recent issue is that of processing of Cu ores with carbonaceous gangue and its negative impact on both recovery and grade.
• Slow flotation kinetics of value minerals due to high presence of coarse middlings. 
   

Guidelines for Lab Evaluation of Flotation Reagents

Copper Ores: Porphyry and Massive Iron Sulfide 

Where high selectivity against pyrite, pyrrhotite, unactivated sphalerite and galena is required under mildly alkaline conditions, short chain dialkyl dithiophosphates such as AEROFLOAT®208 or AEROFLOAT®211 are traditionally used. However, if ore types at a site are highly variable, collector formulations derived from our FM-100 process will prove more robust.  For selectivity against pyrite in chalcopyrite/pyrite ores with or without free milling gold, AERO® 8761  or AERO® 3302  promoters are recommended. If molybdenum is present, AERO® MX-3601  promoter is very effective. AERO® 3416, AERO® 3420, AERO® 7583, and AERO® 3473 are very selective collectors as well. 

For selectivity against arsenic and antimony minerals; AERO® 3404, AERO® 3422 and AEROFLOAT® 208  promoters are useful if copper is associated with penalty minerals such as tennantite.

For rapid flotation kinetics, especially of coarse middlings, improved metals recovery can be achieved using AERO® 7152, AERO® 7249, AERO® MX5144, AERO® 7151, and AERO® MX-950.  Also, aside from choosing a collector, Syensqo recommends exploring frother chemistry to improve metal recovery and flotation kinetics of coarse middling particles.

Compared to xanthates, the selectivity and unique characteristics of Syensqo collectors and collector formulations offer mills greater flexibility in processing of ores and consistency of product performance. Added benefits of Syensqo reagents against xanthates include significant reduction in lime usage, less sensitivity to pulp potential changes and better copper/moly separation  downstream when these reagents and formulations are used at the copper/moly bulk flotation stage. 

When a dithiophosphate becomes the choice for a primary collector, it can be made much more effective when used in conjunction with other custom FM-100 formulations to obtain a synergistic effect. For example, in the case of slightly oxidized or easily tarnished copper ores, AERO® 404, AERO® 407, AERO® 412, AERO® 3739, AERO® 3473, and AERO® 5160 promoters are industry standards in commercial use and can be used in conjunction with xanthate. The new  FM-100 based xanthate replacement AERO® XR products such as AERO® 5160, AERO® 3730, AERO® MX-3753 or AERO® MX-3754  promoters may be a full or partial replacement for xanthate. Best metallurgy is usually obtained when the collectors are added to the grinding mill, or to a lengthy conditioning stage in amounts from 5 g/t to 50 g/t.

In acid circuits, excellent performance has been observed with AERO® 6697, and the AERO® 400 Series promoters. A new product , AERO® MX-3048 promoter, was specifically designed to be a robust sulfide collector in acid circuit conditions. AERO® MX-3048 promoter would be the product of choice for LPF (Leach Precipitation Flotation) flow sheets, or flow sheets that employ flotation of iron sulfides after copper leaching, such as Galvanox  or Sepon  Process. AERO® MX-3048 promoter is very stable under harsh acidic conditions, and does not complex with dissolved metal ions, unlike most collectors. AERO® 6205 is also a good collector for use in acid circuits.

Copper sulfides in massive iron sulfide host are usually finely disseminated with pyrite and pyrrhotite. The intimate mineral associations may require very fine grinding for adequate liberation of the copper minerals. Preference should be given to selective flotation rather than bulk flotation of the sulfides; the rougher concentrate may still require regrinding to achieve satisfactory liberation and concentrate grades. The choice of collectors is similar to that for porphyry copper ores, except that the most selective collectors are utilized. These should include AEROPHINE® 3418 A, AERO® XD-5002, AERO® MAXGOLD 900 and AERO® 7310 promoters and their formulations. The dithiophosphates with short alkyl groups are in use as the principal collectors for ores of this nature. Sodium AEROFLOAT®, AEROFLOAT® 211 or AEROFLOAT® 238 promoters are preferred. The optimum collector chemistry should be established by a systematic laboratory study using a Design of Experiments (DOE) such as a fractional or full factorial laboratory test program (see Guidelines for Laboratory Evaluation of Flotation Reagents ). If necessary, small amounts of an auxiliary collector such as the xanthate replacement formulations (AERO® XR) - AERO® MX-3730, AERO® MX-3752, AERO® MX-3753 and AERO® MX-3754 can be used. Aside from the AERO® XR collectors, AERO® 5100 is also a great auxiliary collector. Stage-addition of collectors may be desirable to enhance selectivity.

For ores with high pyrite and/or pyrrhotite content, increased selectivity is sometimes achieved by the use of sulfur dioxide, alkaline sulfites or metabisulfite . Recently,  several synthetic polymeric depressants have been developed. These have many advantages over the traditionally used depressants in terms of performance, safety, ease of handling, and environmental aspects. Examples of synthetic polymeric depressants are AERO® 7260 HFP  GCA  depressant and AERO® 7261A depressant.

Based on their content of precious metals or oxidized Cu minerals, copper ores can be divided into copper-gold ores or oxide and metallic copper ores, each of which requires a specific approach in processing. The approach for copper-gold ores is detailed in the following section. That of oxide Cu ores can be found here. 

Copper-Gold Ores

For copper ores that contain precious metal values, the collector selection should include AERO® 7152, AERO® 6697, AERO® 5688, AERO® 7249, AERO® 9900, and AERO® 9863  promoters. Also to be considered is the AERO® MAXGOLD 900 promoter family of collectors. AEROPHINE® collectors such as reagent S-7583 have also been found to improve recovery of copper associated with gold. AEROFLOAT® 208 and AEROFLOAT® 238 promoters are also well recognized for recovery of native gold and silver associated with copper minerals. A small amount of xanthate may sometimes be necessary, especially in the scavengers, to maximize recovery. Use of xanthate may be avoided by using AERO® 5160, AERO® 3738, AERO® 3739 or AERO® MX-3753 promoters.  If some of the gold is associated with copper oxide minerals, the use of AERO® OX-100 collectors , in conjunction with the Cu-Au collectors mentioned above, can improve gold recovery.

In any of the copper flotation circuits discussed above, if “slimes” pose a problem by reducing recovery or grade, the use of a slimes dispersant or depressant is highly recommended. Examples include the AERO® 7260 HFP depressant, CYQUEST® 40E antiprecipitant, CYQUEST® 3223 antiprecipitant, CYQUEST® 4000 processing aid either alone or in combination with sodium silicate or soda ash.