C.I. Basilio

A study of the pyrrhotite depression mechanism by diethylenetriamine

Abstract Diethylenetriamine (DETA) is a selective depressant for nickeliferous pyrrhotite during pentlandite flotation. Laboratory flotation tests conducted on ore and process samples showed that pyrrhotite rejection is greatly improved by small additions of DETA; however, the effectiveness of this depressant is most noticeable when the mineral sample is oxidized. LIMS and XPS analyses conducted on flotation products and pyrrhotite specimens showed that the difficulty in pyrrhotite rejection arises from inadvertent activation of the mineral by heavy metal ions, such as Ni2+, Cu2+ and Ag+, that are present in the process water. In the presence of DETA, however, the mineral is deactivated under oxidizing conditions. The deactivation mechanism may involve oxidation of the activation products, which are likely in the form of heavy metal sulfides, followed by solubilization by DETA. FTIR spectra of pyrrhotite electrodes contacted with DETA showed no trace of the reagent on the surface, substantiating the view that its role is one of complexing agent that enhances the dissolution of activation products under oxidizing conditions. FTIR spectra of pyrrhotite contacted with amyl xanthate solutions showed that both dixanthogen and iron xanthate are formed on the surface, the latter becoming more predominant at higher potentials. In the presence of DETA, however, only a small amount of xanthate is adsorbed on the mineral at potentials (Eh) approximately 200 mV higher than the case without DETA.

Lead activation of sphalerite during galena flotation

Abstract Kinetic studies on the flotation of a fine-grained complex lead-zinc ore showed that sphalerite exhibits considerable floatability during the later stages of galena flotation, causing a loss of zinc to lead concentrate. The lead concentrates obtained toward the end of the second lead rougher flotation were examined by X-ray photoelectron spectroscopy (XPS). The results showed that the lead-to-zinc atomic ratios on the surface are significantly higher than in the bulk, suggesting that the flotation of sphalerite is caused by the activation of the mineral by the lead ions present in the flotation pulp. Further evidence of the activation mechanism was given by examining the surfaces of the monominerallic sphalerite specimens that had been immersed in the flotation pulp and other solutions containing lead ions, XPS analysis of the specimens showed significant amounts of lead on the surface. When the specimen was contacted by ore pulp (or simulated plant water) and then with a xanthate solution, the Fourier Transform Infrared (FTIR) spectrum of the specimen showed the presence of lead xanthate and dixanthogen. The proposed activation mechanism is discussed in view of the thermodynamic data available in the literature.

Ethyl xanthate chemisorption isotherms and Eh-pH diagrams for the silver + water + ethyl xanthate system

The interaction of ethyl xanthate with silver electrodes has been investigated by voltammetry, Fourier transform IR spectroscopy, UV-visible spectroscopy and measurements of contact angle under controlled potential. Voltammograms for the silver + ethyl xanthate system display a prewave prior to the formation of a silver xanthate phase. The characteristics of the prewave indicate that it arises from the charge-transfer chemisorption of a monolayer of ethyl xanthate, and this is supported by the changes in solution composition observed during electrochemical treatment. The dependence of the surface coverage of chemisorbed xanthate on potential has been determined from measurements of the charge passed in desorbing the chemisorbed layer formed at equilibrium. The data were found to obey a Frumkin isotherm. Contact angle measurements demonstrate that the chemisorbed xanthate imparts hydrophobicity to the silver surface. An Eh-pH diagram has been constructed that includes the chemisorption process in addition to the formation of silver ethyl xanthate.

A spectroelectrochemical study of chemisorption of ethyl xanthate on gold

Abstract The species formed by the anodic oxidation of ethyl xanthate at gold electrodes has been investigated using an ex situ Fourier transform infrared (FTIR) spectroscopic technique to distinguish between chemisorbed ethyl xanthate and diethyl dixanthogen. Chemisorption of xanthate was found to commence about 0.15 V below the potential at which dixanthogen deposits and to reach a fractional surface coverage of about 0.2 at the reversible value of the xanthate/dixanthogen couple. The coverage increased in parallel with the anodic current arising from dixanthogen deposition. The significance of these findings on the mechanism of the flotation of gold with ethyl xanthate as collector is discussed.

Chemisorption of ethyl xanthate on silver—gold alloys

Abstract The characteristics of the interaction of ethyl xanthate with silver—gold alloys have been compared with those of the pure component metals. Voltammograms for silver and silver—gold alloys (50:50 and 20:80 (wt.%)) in the presence of ethyl xanthate show that xanthate is chemisorbed on silver sites in the alloy surfaces at potentials below those at which silver ethyl xanthate is formed. The coverage of chemisorbed xanthate was determined for the alloys as a function of potential and found to fit the Frumkin isotherm previously derived for silver, when the decreased activity of silver in the alloys was taken into account. The potentials at which finite contact angles developed correlated with those for the onset of chemisorption. It is concluded that the presence of silver in native gold will render gold-bearing ores easier to float with ethyl xanthate as collector.

Chemisorption of ethyl xanthate on copper electrodes

Abstract The interaction of ethyl xanthate with copper electrodes has been investigated by UV-Vis and ex situ FTIR spectroscopies. Xanthate was found to be abstracted from solution in the potential region in which previous studies indicated xanthate to be chemisorbed on copper, and to reappear in solution when the potential was returned to more negative values. The results confidently establish that the process occurring in this potential region is the reversible chemisorption of xanthate. FTIR reflectance spectra characteristic of xanthate were observed after holding the potential at values corresponding to high surface coverage of chemisorbed xanthate, as well as in the region in which bulk copper xanthate deposits. The failure to observe xanthate spectra when medium and low xanthate coverages are present on copper electrodes is shown to result from oxidation of chemisorbed xanthate.

Studies on the use of monothiophosphates for precious metals flotation

Abstract The fundamental mechanisms of dicresyl monothiophosphate (DCMTP) adsorption on gold, silver and gold-silver alloys have been investigated in the present work. The monothiophosphates are obtained by replacing one of the sulfur donors in the functional group of the corresponding dithio derivatives with oxygen. This substitution results in a true acid-circuit collector for bulk sulfide flotation that has also been found to increase gold recovery from primary gold ores. Voltammetric studies indicate that the adsorption of DCMTP is probably the result of a coupled chemical reaction involving an initial electron transfer step (E), followed immediately by a chemical reaction (C). Thus, the adsorption of DCMTP is controlled by both the E h and pK of the system. FTIR spectroscopic and contact angle measurements conducted under controlled potential conditions showed that DCMTP adsorption is potential-dependent. There are no indications of DCMTP adsorption on gold observed in these measurements.

The chemistry and structure-activity relationships for new sulphide collectors

ABSTRACT The chemistry and structure-activity relationships for four new classes of sulfide mineral and precious metals collectors developed recently are discussed in this paper. These collector classes are alkoxycarbonyl alkyl thionocarbamates and thioureas, dialkyl (or diaryl) monothiophosphates and dialkyl monothiophosphinates. The main emphasis will be to highlight the differences between collectors and their affinities for various minerals on the basis of data on kinetics of adsorption on pure minerals, natural ore flotation and microscopy of flotation concentrates. The mechanism of interaction of these collectors with sulfide minerals is also discussed with the available data on the FTIR and solution chemistry studies.

Thermodynamics of chalcocite-xanthate interactions

Abstract Eh-pH diagrams have been constructed for chalcocite in the presence of xanthate. Stability regions for cuprous xanthate have been shown to be dependent on the sulfur oxidation state. As oxidation proceeded from elemental sulfur to sulfate, the copper xanthate stability region under alkaline conditions extended to lower potentials. The voltammograms indicated that xanthate reacted with chalcocite to form cuprous xanthate and a nonstoichiometric copper sulfide starting near −40 mV. This is in agreement with the thermodynamic calculations made for the case involving oxidation to elemental sulfur. However, the voltammograms showed that the initial xanthate adsorption peak, which is attributed to chemisorbed xanthate, started between −275 and −295 mV. Based on this information, chemisorbed xanthate is calculated to have a standard free energy relative to the xanthate ion of between −12.6 and −13.1 kcal/mol.

Development of the chemical and electrochemical coal cleaning process. Technical progress report, October 1, 1991--December 31, 1991

The continuous testing of the Chemical and Electrochemical Coal Cleaning (CECC) bench-scale unit (Task 6) was completed successfully in this quarter using Middle Wyodak and Elkhorn No. 3 coal samples. The CECC unit was run under the optimum conditions established for these coal samples in Task 4. For the Middle Wyodak coal, the ash content was reduced from 6.96% to as low 1.61%, corresponding to an ash rejection (by weight) of about 83%. The ash and sulfur contents of the Elkhorn No. 3 coal were reduced to as low as 1.8% and 0.9%. The average ash and sulfur rejections were calculated to be around 84% and 47%. The CECC continuous unit was used to treat -325 mesh Elkhorn No. 3 coal samples and gave ash and sulfur rejection values of as high as 77% and 66%. In these test, the clean -325 mesh coal particles were separated from the liberated mineral matter through microbubble column flotation, instead of wet-screening.