Executive Summary
Management of sulfide gangue like arsenopyrite and pyrrhotite in complex ores as well as in Cu-Ni ores is essential to achieving concentrate grades and avoiding smelter penalties. An approach to dealing with sulfide gangue is to use a selective collector that preferentially floats value sulfide minerals and not sulfide gangue. However, use of a selective collector is often not enough and depressants are required to sharpen the separation.
Syensqo offers AERO® 7261A, a unique depressant that has demonstrated to be effective at reducing both arsenopyrite and pyrrhotite flotation. In addition, AERO® 7261A has an excellent health, safety and environmental profile relative to inorganic depressants. The following discusses some of the major considerations and challenges faced when dealing with arsenopyrite and pyrrhotite in the context of complex- or Cu-Ni ores. Examples for each of these ore types are given which feature the positive impact that AERO 7261A had regarding depression of the above-mentioned sulfide gangue minerals.
General Comments / Major Considerations
The presence of sulfide gangue minerals, arsenopyrite (AsPy) and pyrrhotite (Po) in an ore can often be problematic, particularly in some complex sulfide separations as well as in Cu-Ni ores (mainly Po). Syensqo has developed a unique synthetic depressant, AERO® 7261A Depressant, that can be effective in reducing AsPy and Po flotation. AERO® 7261A has the advantage of excellent toxicological and environmental characteristics.
Challenges Faced
Excessive levels of arsenic in concentrate can result in penalties or even rejection of the concentrate by the smelter, with requirements tightening over time. High levels of pyrrhotite, even if floatability is limited, can still result in lower grade concentrates. These complex sulfide ores are frequently characterized by very fine grain size, with the need to grind to very fine size to achieve good liberation. Depending on the value minerals present, there is also the risk of activation of the AsPy/Po in the grind/regrind, by Cu or Pb ions, exacerbating the problem. With the fine grinds comes the issue that entrainment of AsPy and Po can be high.
An essential step is to identify the predominant arsenic species. This solution is effective for arsenopyrite, however if the arsenic is present as tennantite, enargite, proustite, etc., then the solution is less effective and may be undesirable, due to Cu or Ag losses. It should also be determined if any values are associated with the arsenopyrite, such as Au/Ag. In this case, AsPy depression may not be desirable. Similarly, in Cu-Ni operations, it is important to know how much Ni and in what form is present in Po, given that, Po depression may potentially result in Ni losses.
Traditional Strategies / Syensqo Recommendations
Arsenopyrite and pyrrhotite can be depressed to a reasonable degree under high lime conditions. However, this can sometimes reduce the efficiency of the value mineral flotation, if it takes pH out of the optimum window of effectiveness. Alternative depressants are inorganic molecules, such as diethylene triamine (DETA), triethylene triamine (TETA), and sodium cyanide (NaCN). The main drawback of these inorganic depressants, however, is that they are difficult to handle and hazardous to people and the environment.
Depressants are usually the second option when it comes to controlling problematic sulfide gangue. Typically the best option for control of sulfide gangue is through use of a selective collector, such as AEROPHINE® 3418A. The selective collector can effectively float the value minerals with minimal activation of gangue sulfides, such as AsPy and Po. Sometimes, however, this is not quite enough and the combination of selective collector and depressant is required, as in the case given below for Pb/Zn flotation.
Syensqo's solution is the addition of AERO® 7261A Depressant to depress AsPy and Po. This has the advantages that it need only be applied when required and dosage can also be tailored to requirements, giving greater control. It also has excellent toxicological and environmental properties and being a liquid product is very easy to handle and apply. AERO® 7261A can be dosed neat or applied as a 2%-20% solution.
An example is where AERO® 7261A has proven an effective depressant for arsenopyrite and pyrrhotite in Pb/Zn flotation, on both circuits. Use of AERO® 7261A has reduced arsenic penalties by rejection of arsenopyrite and improved concentrate grades through depression of pyrrhotite.
Due to the very fine grain size, AERO® 7261A depressant is added following regrind of rougher concentrates. Recommended dosage is around 200-400 g/t on a stage basis. Optimum pH is in the range 9.0-10.8, though effectiveness is maintained at the higher pH utilized for Zn flotation. Further AERO® 7261A additions can be made in later cleaning stages to maximize effectiveness. AERO® 7261A shows excellent selectivity as it shows minimal depression of the values, even when dosage is increased above normal operational levels.
Po depression without impact on Ni recovery has also been observed in Cu-Ni ores. An example of this is shown in Figure 1 for a massive sulfide ore in which it is clear that use of AERO® 7261A leads to effective depression of Po and, in addition, results in higher recovery of pentlandite (the main Ni mineral). For comparison, the curves for tests using TETA and TETA in combination with sodium metabisulfite (SMBS) are also shown. The advantages of using AERO® 7261A relative to these alternative depressant schemes are twofold: 1) one avoids the use of TETA, which is deemed not to be environmentally benign, and 2) there is no need to control two separate reagents in application of the depressant.
