The use of enrichment ratios to support kinetic studies in flotation

• Published in: Minerals engineering 2019-12, Vol.144 (C), p.106054, Article 106054
• Main Authors: Vinnett, L., da Silva, G.R., Marion, C., Carrasco, C., Waters, K.E.
• Format: Article
• Language: English
• Subjects: Enrichment ratio; Entrainment; Flotation kinetics; Mineral recovery
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2019.106054

•Enrichment ratios (ER) were studied from batch flotation kinetics.•Incremental ERs along with the Agar’s criterion allowed R∞ to be assessed.•Discrete ERs greater than 1 were typically observed for long flotation times.•Size-by-size analyses showed the same trend even in the finer fractions.•True flotation cannot be rejected as a recovery mechanism at the end of the tests. This paper presents the use and evaluation of enrichment ratios (ER) from different batch flotation protocols. Two protocols under flotation time extensions (>20 min) are analysed, which favour steady recoveries to be obtained at the end of the process. Agar’s criterion is used to evaluate the consistency between the maximum recovery obtained by regression and the total measured recoveries. A good agreement is observed under critical flotation times (tcrit) lower than 40% of the total flotation time, where tcrit corresponds to the time at which the incremental concentrate grade equals the feed grade (grinding product). A discretized ER is used as an approximation of instantaneous ER to characterize the evolution of the enrichment along the process. This discrete ER is defined as the ratio between the incremental concentrate grade and the grade of the solid in the flotation cell prior to the respective flotation interval. Discrete ERs greater than 1 along with significant discrete recoveries are feasible, suggesting that further analyses are required to evaluate the process exhaustion. Four size-by-size tests are also studied to assess the distribution of the discrete ERs at long flotation times. Almost all the evaluated classes present discrete ERs greater than 1 in the last flotation intervals. Therefore, the non-selective mechanisms (i.e., entrainment, true flotation of gangue and gangue association) cannot be considered as the predominant contributions to the overall discrete recoveries. Exceptions may be laboratory tests under very fast kinetic responses, high mass recoveries, long flotation times and high content of non-floatable valuable minerals.