Mitigating the deleterious effect of clay minerals on copper flotation

Abstract

Clay minerals have a deleterious effect on the mineral flotation process. Generally, two major phenomena are observed in industry when processing high clay ores: no froth formed on the top of the pulp phase and few valuable minerals loaded on the top of froth. This is an ARC Linkage project with support from Pionera, a reagent company manufacturing biopolymers. The objective of the project is to define the different effects of clay minerals on copper flotation, and then to mitigate the deleterious effects of specific clay minerals in copper flotation by biopolymers and other means. In this research, two types of clay minerals, swelling bentonite with a 2:1 structure and non-swelling kaolinite Q38 with a 1:1 structure, were chosen to represent two typical kinds of clay minerals often seen in industrial flotation plants. The influence of bentonite and kaolinite on copper flotation was investigated. It was found that bentonite and kaolinite affected the copper flotation in a different way. Increasing the proportion of bentonite increased the pulp viscosity that reduced the amount of froth on the top of slurry and decreased flotation rate, resulting in a lower copper recovery. On the other hand, increasing the kaolinite content mainly decreased the copper grade by entrainment that is characterised by smaller bubble size and higher froth stability. The different roles of bentonite and kaolinite in the flotation were associated with their unique structure properties. Also, the collector and frother dosage plays an important role in specifying the different effect of bentonite and kaolinite on copper flotation performance. To mitigate the deleterious effect of kaolinite, three lignosulfonate biopolymers from Pionera, DP-1775, DP-1777 and DP-1778 with different structures, were examined. While rheological measurements indicated that these biopolymers dispersed the kaolinite aggregates, a beneficial effect of biopolymers on copper flotation in the presence of kaolinite was not observed. Instead, interactions of biopolymers with the frother appeared to enhance the froth stability and therefore further reduced copper grade by mechanical entrainment. Two-phase foam characterization revealed that the foam height increased in the blends of biopolymers with the frother. The dispersing and foaming abilities of biopolymers were governed by their structure features such as the content of functional groups, the molecular weight and counterions. The three biopolymers, DP-1775, DP-1777 and DP-1778, were also tested to reduce the negative effect of bentonite in copper flotation. Rheological measurements indicated that all of the three biopolymers could not significantly reduce the pulp viscosity which was dictated by bentonite. This is consistent with the observation that none of the three biopolymers could enhance the copper recovery effectively. Electrolytes were then used to mitigate the deleterious effect of bentonite on copper flotation through reducing the high pulp viscosity. It was found that with Cl- or SO_4^(2-) being an anion, Na+, K+, Mg2+ and Ca2+ cations had a different effect on pulp viscosity and copper flotation. At the same salt concentration, divalent cations, Mg2+ and Ca2+, were more effective than monovalent cations, Na+ and K+, in reducing bentonite viscosity and therefore increasing copper recovery. Compared with cations, there was little difference between anions, Cl- and SO_4^(2-), in reducing bentonite viscosity and improving copper recovery. Overall, the results of this thesis study clearly show that kaolinite and bentonite negatively affected copper flotation in a different way, due to their different structures. Thus, different solutions should be applied to deal with their negative effects. While salts have the potential to mitigate the deleterious effect of bentonite in copper flotation, biopolymers with new structures may be designed to mitigate the deleterious effects of both kaolinite and bentonite based on the thesis study.