An apparatus to measure electrical charge of bubble swarms.

An apparatus has been developed to characterize bubble charge by measuring the swarm potential of gas bubbles. The technique allows in-process measurement of all system variables associated with bubble surface electrical charge: swarm potential, solution conductivity, gas holdup, pH and bubble size distribution. The method was validated by comparing with literature iso-electric point (iep) values. Bubble swarm potential was measured as a function of concentration and pH for a series of non-ionic surfactant frothers, ionic surfactant collectors and multivalent metal ions. Results showed good agreement with established theory and prior experimental findings. The setup is a step towards measurement of charge on flotation size range of bubble swarms.

Using sound to study bubble coalescence.

Frothers are surfactants used in flotation to aid generation of small bubbles, an effect attributed to coalescence prevention. Studying coalescence at the moment of bubble creation is a challenge because events occur over a time frame of milliseconds. This communication introduces a novel acoustic technique to study coalescence as bubbles are generated at a capillary. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has the resolution to detect events that occur within 1-2 ms. The results show that for common flotation frothers and n-alcohols (C(4)-C(8)) coalescence prevention is not simply related to surface activity. A total stress model is used to give a qualitative explanation to the action observed. Results for salt (sodium chloride) are included for comparison.

Processing of metallurgical residues by flotation - bench-scale studies on two industrial products.

Resource recovery from two metallurgical residues by flotation was investigated applying an electrostatic model to select initial conditions. The first, a sulphation roast/water leach residue, was processed to float lead sulphate, comparing dodecylamine and xanthate collectors. From the second, a neutralization residue, gypsum, was recovered by reverse flotation of ferric hydroxide, comparing oleate and sulphonate collectors. In both cases, further upgrading by acid leaching was considered.

Measurement of thickness and composition of a solvent film on a bubble.

Solvent-coated air bubbles in the air-assisted solvent extraction (AASX) process achieve the dual role of high solvent specific surface area and ease of phase separation. The properties and thickness of the solvent film control the process. As an approach to the study, the layer interferometry (in the UV-vis region) and FT-IR spectroscopy were used to measure the time dependent thickness and chemical composition, respectively, of a film formed by blowing an air bubble in kerosene-based solvents. The film was stabilized by the presence of 1.5 ppm silicone oil, as employed in AASX. The film appears to comprise two layers; an outer layer of almost constant thickness and an inner layer which decreased in thickness with time. The latter is considered relevant to AASX. Generally, the initial thickness was approximately 3 microm which decreased over several minutes to a final rupture thickness of 500 nm. The initial thickness is of the order determined indirectly. The chemical composition of the layer did not change with time.

Aggregation of sphalerite: role of zinc ions.

Sphalerite from six sources is shown to aggregate at ca. pH 7-9, confirmed by different techniques (settling velocity, suspension analysis, and optical microscopy). This does not correlate with the isoelectric point, which is consistently < pH 6. A similar observation was made by Healy and Jellet [J. Colloid Interface Sci. 24 (1967) 41-46] for ZnO (and reconfirmed here), who suggested Zn hydrolysis products were responsible. The hypothesis is tested using chalcopyrite and silica suspensions in the presence of Zn ions. It is found that aggregation occurs over the same pH range, 7-9. Solution and surface analysis (extraction by EDTA) shows sphalerite released sufficient Zn ions to promote aggregation. The pH range 7-9 corresponds to hydroxide formation, suggesting this is the species responsible. Aggregation of sphalerite due to the polymerization/flocculation action of zinc hydroxide is proposed.

A useful UV spectroscopic method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions.

An alternative method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions is described. This method is based on the formation of a DETA-Ni(II)-sulphite complex, which shows a UV absorption maximum at 285 nm that varies linearly with the concentration of DETA throughout the 0-50 mg l(-1) DETA range. A high concentration of Ni(II) is used to offset the effect of any Cu(II) or Ni(II) ions that may already be present in the industrial plant solutions under analysis. The intensity of the absorbance maximum is dependent on the sulphite ion concentration, but this problem is overcome by measuring the absorbances when the test solutions are spiked with different concentrations of DETA and then extrapolating the absorbance versus DETA concentration plot to zero absorbance to obtain the original concentration of DETA in the test solutions.