Elsevier

Minerals Engineering

Volume 81, 1 October 2015, Pages 152-160
Minerals Engineering

Study of froth behaviour in a controlled plant environment – Part 1: Effect of air flow rate and froth depth

https://doi.org/10.1016/j.mineng.2015.07.003Get rights and content

Highlights

  • A device is developed to determine the recovery of collection and froth zones in a controlled plant environment.

  • Air rate has a positive effect on recovery of particles in both the collection and froth zones.

  • Deep froth causes the weakly composite particles to drop out of the froth.

  • Froth recovery is a strong function of particle size.

Abstract

This paper presents the results of a thorough investigation into the froth recovery measurements in a controlled plant environment using a device that allows direct collection of dropback particles from the froth phase.

Experiments were performed at the Northparkes concentrator (NSW, Australia), using a feed taken from the head of the cleaner scavenger bank. The feed slurry had a relatively higher copper grade varying from 5.2% to 6.8%. Experiments were performed to investigate the effect of important flotation parameters such as air flow rate and froth depth, on the froth performance. The size of the particles in the relevant streams was analysed to acquire in-depth knowledge about the froth dropback mechanism. The results suggested that the froth recovery could be as low as 70%, although it was relatively easy to achieve the values in the range 75–85% by the correct choice of operating variables. It was found that the air flow rate has a positive impact on both collection (pulp) and froth zone recoveries. However, the effect was more prominent in the froth zone. It appeared that the froth recovery is a strong function of particle size.

Introduction

Froth flotation is an important mineral concentration process that exploits the physicochemical surface properties of mineral particles to separate the valuable minerals from the waste rock. Two distinct zones are evident in a flotation cell: the pulp zone and the froth zone. The pulp zone provides a platform for an efficient bubble–particle-attachment while the froth zone plays an important role in upgrading the final concentrate.

The efficiency of froth phase is often defined by the term froth recovery. A number of techniques have been developed over the past few decades to determine froth recovery. These techniques can be broadly divided into two categories: Indirect methods that include model fitting; correlation of froth recovery with flotation rate constant and froth retention time; mass balancing across the flotation cell (Alexander et al., 2003, Savassi et al., 1997, Vera et al., 1999, Yianatos et al., 2008, Neethling, 2008) and direct methods. Two types of direct froth recovery measurement methods currently present in the mineral industry are bubble load and modified column or froth dropback methods (Falutsu and Dobby, 1989, Seaman et al., 2004).

Recently, we have developed a laboratory-scale device to measure froth performance (Rahman et al., 2012). The device permits independent measurement of froth recovery by collecting the particles dropping out of the froth zone. Flotation feeds were prepared as mixtures of silica (quartz) particles of two size ranges: 60G (‘fine’ particles, d80 = 72 μm) and 50N silica (‘coarse’ particles, d80 = 299 μm), in varying proportions, at a constant total solids concentration of 20% w/w. The fraction of fines in the feeds was varied from 40% to 95%. The silica used in the study was fully liberated. As a result, no composites were present, and the effect of various variables on the froth behaviour were investigated. Following on from this work, similar experiments were attempted in a laboratory cell using raw samples received from the Northparkes mine (NSW, Australia). The ore was first ground, treated with reagents and then fed continuously into the laboratory cell. However, the grade of the feed samples was low, and the number of tests required to capture sufficient concentrate solids for meaningful analysis was found to be extremely time-consuming. It was, therefore, decided to move the laboratory rig to the Northparkes concentrator, and to conduct experiments using the feed from the cleaner/scavenger, which had a grade in the order of around 7% copper, that would generate a concentrate flowrate sufficient enough for subsequent analysis. The influence of air flow rate, froth depth, collector concentration, and frother concentration on the froth performance was investigated. The variation of froth recovery as a function of particle size and a comparison of the copper grade of feed, tailings, dropback and concentrate samples were also provided in order to acquire an in-depth knowledge of froth behaviour. This paper presents the results of the influence of operating parameters (air flow rate and froth depth) on the froth recovery while the effect of frother and collector concentration on the froth recovery will be given in a following study.

Section snippets

Flotation feed ore

To perform independent flotation experiments in a controlled environment, feed slurry samples were collected from the cleaner-scavenger feed stream of Module 1 of the Northparkes flotation circuit. The slurry collection point in the Module 1 flotation circuit is shown in Fig. 1. The feed contains primarily chalcopyrite (CuFeS2) and bornite (Cu5FeS4) with small amounts of chalcocite and covellite. The feed at the time of testing had a relatively high copper grade that varied from 5.20% to 6.76%,

Treatment of raw experimental data

After the flotation experiments were completed, the slurry flow, dry solid mass and assay data for each of the experimental samples were compiled. The raw experimental data were then subjected to error minimization analysis for correction. The overall mass balance was achieved initially by considering the overall slurry flowrate, solid mass and copper assay data of feed, tailings, dropback and concentrate. By using the corrected overall solid mass, along with size distribution and copper assay

Effect of air rate

Experiments were undertaken to study the effect of air rate on the froth-phase behaviour. Superficial gas velocities (Jg) used were, 1 cm/s, 1.4 cm/s, 1.8 cm/s and 2.1 cm/s. Two consecutive runs, Runs 1 and 2, were carried out to follow the recovery trend with changes in Jg. The froth depth was maintained at 240 mm during the experiments. No further chemical reagents were added to the conditioned feed slurry collected from the flotation circuit.

Conclusions

The froth dropback device developed in our laboratory (Rahman et al., 2012) was used to measure froth recovery in a controlled plant environment. The froth dropback device was trialled at the Northparkes Mine, where a continuous supply of plant chalcopyrite enriched feed slurry was assured. The effect of air flow rate and froth depth on froth recovery were investigated.

The results showed that the froth phase has a significant role in the flotation process. It was found that froth recovery of

Acknowledgments

Financial support from the sponsors of the AMIRA (Australian Mineral Industry Research Association) Project P90 is greatly acknowledged. The authors wish to thank Kitty Tang, Cagri Emer and Ghislain Bournival for their contribution to the testwork. The authors would also like to acknowledge the support from the Northparkes concentrator personnel during the testwork, especially Jaclyn McMaster, Tom Rivett and Heather Gault.

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