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A chemical method for removing calcium sulfate saturated solutions (0.016 mol/L CaSO4) using barium chloride (BaCl2·2H2O) and sodium phosphate (Na3PO4) was experimentally studied. The main interest is to remove these ions from the solution through the precipitation of two solid species: sulfate (SO42−) as barite (BaSO4), and calcium (Ca2+) as hydroxyapatite (Ca5(PO4)3OH). Additionally, a solid/liquid separation method (i.e., flotation) was explored, using oleic acid and dodecylamine as collectors. The results show that, the chemical treatment of saturated solutions at 60 °C, pH 11.5 and using 3.9 g/L BaCl2·2H2O and 1.6 g/L Na3PO4, promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite (Ca10–x(HPO4)x(PO4)6–x(OH)2–x), with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L, respectively. The residual calcium concentration increases to 28 mg/L when using the same amount of reactants, at temperature and pH values below those quoted. The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%, while that of barite floated with dodecylamine at pH 6.5 was about 90%.

Entre los agentes quelantes destacan los ácidos hidroxámicos, los cuales han mostrado un rendimiento superior sin las preocupaciones de salud, seguridad y medio ambiente asociadas con los xantatos. En este estudio se evaluó y comparó mediante espectroscopia infrarroja y mediciones de potencial zeta, la adsorción química de dos hidroxamatos, sobre la superficie de la anglesita. Asimismo, se efectuaron mediciones de microflotación para evaluar y comparar su respuesta a la flotación. Finalmente, se propusieron los mecanismos de interacción entre la anglesita con los aniones hidroxamato en solución acuosa, los cuales presentan reacciones globales y ayudan a entender la manera en que reaccionan ambos colectores. En general, las pruebas de microflotación mostraron mayores recuperaciones de anglesita usando AOH. Se sugiere que los aniones benzohidroxamato y octanohidroxamato se adsorben químicamente sobre la anglesita en la mayoría de las condiciones estudiadas, excepto sobre la anglesita acondicionda a pH 5, en donde se encuentran fisisorbidos.

Currently there is a wide variety of collectors used in mineral processing, the xanthates being the most used in sulfides flotation. Unfortunately, it is known that xanthates are not stable compounds and their decomposition generates carbon disulfide (CS2), a substance that is considered toxic. These aspects have motivated the search for collectors that exhibit superior performance without the health, safety and environmental (HSE) concerns associated with xanthates. In this study, the chemical stability of three xanthates of different alkyl groups (sodium ethyl xanthate (SEX), sodium isopropyl xanthate (SIPX) and potassium amyl xanthate (PAX)) was evaluated by UV/Vis spectroscopy, as a function of pH and time. Similarly, the chemical stability of three chelating collectors was evaluated: sodium di-isobutyl dithiophosphinate (SDIBDTPI), benzohydroxamic acid (BHA) and octanohydroxamic acid (OHA). Likewise, the surface tension of their aqueous solutions was measured making use of the Du Nouy method, to determine the critical micelle concentration (CMC). The results showed that the xanthate UV/Vis absorption spectra reflect the presence of a chemical reaction as the pH decreases from 4 to 2.5, which results in the formation of carbon disulfide (CS2). In addition, the generation of CS2 is favored as time elapses and the pH of the solutions decreases from 10 to 6, regardless of the hydrocarbon chain length. Conversely, dithiophosphinate and hydroxamic acids present greater chemical stability, although they form micelles at a certain concentration (CMC), a phenomenon that is not observed with xanthates. By not hydrolyzing, oxidizing, or decomposing into other chemical species, SDIBDTPI, BHA, and OHA may be considered environmentally friendly reagents. In the above context, it is important to promote the adoption of these collectors in mineral processing.

In the concentrators of a Mexican mining company has been observed that the pH of the flotation has a significant effect on the galena recovery: the increase of pH from 7.5 to 9.5 in the Pb/Cu flotation circuit, resulted in a decrease of about 10% of lead recovery. In the present investigation, experimental models and techniques were developed to study the effect of pH on xanthate and di-isobutyl dithiophosphinate adsorption onto galena. The results obtained by UV / Vis spectroscopy showed that once galena surface has been slightly oxidised by the dissolved oxygen of the aqueous suspension, adsorption of both surfactants increases significantly, being adversely affected by the increase of pH from 5.5 to 9.5. Microflotation measurements performed for both surfactants support these findings. Thermodynamic simulation of the system suggests that the observed behaviour is due to the nature of the solid species formed on the galena surface at the particular pH: lead sulfate (PbSO4) under neutral and sli...

This paper presents and discusses measurements performed to study the interaction mechanism of calcium and sulfate with galena and their effect on xanthate adsorption. The results of collector adsorption show that regardless of the solution pH (5.5, 7.5 and 9.5), the presence of calcium and sulfate during the mineral pre-conditioning, decreases the adsorption of isopropyl xanthate onto galena. Microflotation measurements carried out at pH 9.5 show that at low concentrations of calcium and sulfate (below about 0.005 mol/L), the recovery of galena is not affected. However, as the concentration of both ions increases, flotation recovery substantially decreases. Contact angle measurements corroborate this behavior: a relatively large contact angle in the absence of calcium and sulfate (i.e., 64°), and a significant decrease when these species are present (i.e., ca. 45°). The observed behavior suggests that calcium ion probably has a certain chemical affinity for the active sites of the galena, which hinders the occurrence of ion exchange collector-sulfate or collector-hydroxyl to form lead xanthate (PbX2), which is the species responsible for the enhanced hydrophobicity of the mineral. On the other hand, the adverse effect of the sulfate is probably due to the formation of a layer of lead sulfate on the galena surface, which acts as a barrier that hinders the interaction of the collector with the metallic sites of the mineral lattice, thus negatively affecting the chemisorption mechanism. Likewise, the decreasing of lead concentration in solution, in equilibrium with the precipitated PbSO4 and the sulfate, limits the precipitation/coagulation of lead xanthate in the vicinity of the interface. Electrochemical measurements corroborate the proposed mechanism.

A study of the electrochemical behavior of galena and the effect of the Ca2+ and SO42− species on the mineral behavior at different pH, was carried out using carbon paste electrodes. The Ca2+ and SO42− ions were used to simulate the species that are most concentrated in the recycled water of sulfide mineral flotation processes. By means of electrochemical and SEM analysis, it was possible to identify the chemical species that are generated on the mineral surface by means of redox reactions. In the same way, it was observed that depending on the pH, Ca2+ and CaOH+ species interact with the oxidized species of galena. Furthermore, at acidic pH, sulfate reacts with lead ions to form a passivating layer on the surface of the mineral, while at alkaline pH more than one species is generated on the mineral, which passivate its surface.

Currently, the mineral processing industry faces major challenges in the development and implementation of strategies and new processes for the recovery of lead from low-grade oxidized minerals, such as cerussite (PbCO3) and anglesite (PbSO4). In this study, the behavior of the individual flotation of galena (PbS), cerussite (PbCO3) and anglesite (PbSO4), without sulfidation, was investigated using benzohydroxamic acid (BHA) and octanohydroxamic acid (OHA) as collectors. Spectroscopy UV/Vis measurements were carried out to investigate the effect of pH on the adsorption of both collectors on the surface of these minerals. Likewise, contact angle measurements were conducted to evaluate the hydrophobicity imparted to the minerals. Furthermore, the selectivity of both collectors towards quartz (SiO2) and pyrite (FeS2), mineral species commonly found as gangue, was evaluated. Overall, microflotation tests showed higher recoveries of galena, cerussite and anglesite using OHA. Anglesite proved to be the most challenging mineral to float, probably because it is the most soluble of the three lead minerals tested. It requires higher dosages of OHA and the presence of sulfate (e.g., to reduce its solubility) to show good recoveries under slightly acidic conditions. Also, the recoveries of cerussite and anglesite were affected under alkaline conditions. Thermodynamic modeling suggests that the observed behavior is due to the presence of hydrocerussite (Pb3(CO3)2(OH)2), of hydrophilic nature, on the mineral surfaces. OHA proved to be the most effective collector; nevertheless, it also showed significant loss of selectivity against pyrite, although not against quartz, so its use will depend on the nature of the gangue present in the ore to be treated. BHA neither floats quartz nor pyrite. Therefore, BHA could be considered a potential candidate for the flotation of galena and cerussite due to its high selectivity. In summary, the use of hydroxamates would mitigate the impact on health and the environment that results from the use of xanthates.