Improving sulphide-mineral flotation with sustainable cellulose-based frother formulations

Froth flotation is still the most prominent mineral enrichiment process, though its origins are over a century old. Its ample popularity is based on versatile, yet effective operations, and favorable cost efficiency. Despite the historical success of the process, the trend of decreasing grades in available ore bodies, as well as increasing environmental awareness are driving the mining industry towards a new era of sustainable and efficient operations. The present work aims to contribute towards this end by proposing a fundamentally novel type of frother formulation, where typical frothers are partly substituted with a nontoxic and biodegradable cellulose derivative, namely hydroxypropyl methyl cellulose (HPMC), thus forming an interactive polymer-surfactant (PS) mixture. Considering that there are no earlier reports of this specific PS-mixture and that this kind of an approach had not been explored before in flotation, this thesis presents the first ever scientific investigation to evaluate the applicability of this novel chemistry to be used as reagents in mineral froth flotation. All aspects of this study contain a comparison between two commercial frothers (DowFroth 200 and NasFroth 240), HPMC and their corresponding PS-mixtures. The first part of this study is focused on interfacial characterization of the PS-mixtures in terms of properties relevant to flotation, i.e., dynamic surface tension, bubble size, foam depth and foam stability. The short-term diffusivity of each species was determined based on the surface tension results. The second part of this study consists of three flotation campaigns conducted with i) natural Cu ore; ii) synthetic Cu ore and synthetic Zn ore, iii) Cu containing tailings. The results of this thesis show that PS-mixtures exhibit a distinct behavior at the air-liquid interfaces compared with single surfactant species used as commercial frothers. In the first place, the interactions between HPMC and NasFroth 240 resulted in a faster adsorption rate of the PS-complex, which was responsible of generating smaller bubbles that were liklely maintained by the steric protection provided by the polymeric component. Furthermore, the presence of HPMC improved foam stability both in single species systems and as a part of a PS-mixture. The observed PS-synergism and its effect on interfacial properties showed clear improvements in flotation performance in all aspects of this thesis. The main advantages were observed as improvements recovery and flotation kinetics, which were connected to a combination of improved froth stability and reduced bubble sizes. Furthermore, the self-stability provided by the PS-mixture helped to maintain a steady level of performance in conditions considered detrimental to flotation (e.g., significantly lower collector concentration or deviance in pH level). Ultimately, the findings of this thesis indicate the possibility of increasing throughputs by only changing flotation chemistry and exploring novel circuit design or flotation chemicals whose application requires an increased froth stability that is less dependent on mineral hydrophobicity.