P. De Donato

Mechanism of oleate interaction on salt-type minerals. IV, Adsorption, electrokinetic, and diffuse reflectance FT-IR studies of natural fluorite in the presence of sodium oleate

Abstract The mechanism of oleate interaction with fluorite is investigated through adsorption, electrokinetic, and diffuse reflectance FT-IR measurements coupled with theoretical thermodynamic chemical equilibrium calculations. The adsorption isotherms exhibit an infinite increase in the slope beyond an oleate density of 10 μmole m−2. This adsorption density corresponds to a bilayer formation of oleate by two-dimensional condensation with a reported molecular coverage area of 33A˚2 (liquid-crystal state). Comparison of the theoretical chemical equilibria with the experimental data shows that the infinite increase in the slope of the isotherms is due to the precipitation of calcium oleate. The solubility product of this three-dimensional phase is found to be in the pK range 14.4–14.5, and agrees with most of the values quoted in the literature. From IR studies, monocoordination of oleate through counter sodium and calcium ions is suggested for the monolayer filling. ζ potentials of fluorite are correlated to the adsorption of oleate up to bilayer formation, and formation on surface of calcium oleate (three-dimensional growth on substrate) at high oleate concentrations. Two-dimensional condensation of oleate on the fluorite surface followed by the association of hydrocarbon chains (tail—tail bond) for the second layer, prior to the precipitation of calcium oleate in the bulk solution, is proposed as the adsorption mechanism.

Interaction between finely ground galena and pyrite with potassium amylxanthate in relation to flotation, 2. Influence of grinding media at natural pH

Abstract Diffuse reflectance Fourier transform infrared (FTIR) spectroscopy, Hallimond tube flotation cell and microelectrophoresis have been utilized to investigate the reactions involved in the adsorption-abstraction of K-amylxanthate on finely ground galena and pyrite. In order to work under well controlled conditions, pure minerals were wet ground in specially built laboratory stainless steel and iron rod mills. X-ray photoelectron spectroscopic (XPS) studies have been carried out in order to characterize the surface oxidation products after grinding. According to collector concentration, the following surface products were found to be formed on galena: monocoordinate lead xanthate, non-stoichiometric and stoichiometric lead xanthate, dixanthogen and amylcarbonate disulphide. Only dixanthogen was observed on pyrite after using stainless steel rods, while ferric iron xanthate and physically absorbed xanthate ions were found to be formed when iron rods were utilized. The use of iron grinding media slightly depresses the floatability of galena and pyrite.

Interaction of finely ground galena and potassium amylxanthate in flotation, 1. Influence of alkaline grinding

Abstract Diffuse reflectance Fourier transform infrared spectroscopy, Hallimond tube flotation cell and microelectrophoresis have been utilized to investigate the reactions involved in the adsorption-abstraction of K-amylxanthate on finely ground galena. The mineral was ground in a laboratory stainless steel rod mill in basic conditions (pH 11.0 and 12.5). pH regulators were NaOH and CaO. A two-stage adsorption process was discovered for amylxanthate at pH 11.0. During the first stage a mixed layer is formed. For low concentrations or submonolayer capacity it is made of 1:1 monocoordinated lead xanthate and dixanthogen; for surface coverage up to 5.4 it is composed of nonstoichiometric lead xanthate, amyldixanthogen and amylcarbonate disulphide. In the second stage, mainly amyldixanthogen is formed; at high xanthate concentration (1×10 −2 mole per dm 3 ) 1:2 coordinated lead xanthate is formed in addition. The second-stage process corresponds to complete flotation and to a sharp decrease in zeta potentials.

FTIR analysis of sulphide mineral surfaces before and after collection: galena

Abstract Modern IR instruments such as interferometers used with diffuse reflectance accessories or “in situ” ATR experiments allow the characterization of the state of sulphide mineral surfaces and specially galena after wet or dry grinding and collection with xanthates. After dry grinding only lead xanthate, either monocoordinated or in the three dimensional form, is formed depending on the initial xanthate concentration. Wet grinding leads to heterogeneous adsorbed layer formed with monocoordinated lead xanthate and dixanthogen at low concentrations (monolayer domain), stoichiometric or non-stoichiometric lead xanthate, dixanthogen, and the dimer of the monothiocarbonate for higher concentrations.

An infrared investigation of amylxanthate adsorption by pyrite after wet grinding at natural and acid pH

Abstract Batch adsorption tests and Fourier transform infrared spectroscopy with diffuse reflectance have been used to investigate the adsorption/abstraction from amylxanthate solutions on the surface of freshly ground pyrite in natural and acidic (pH 4.0) conditions. The species formed are mainly dixanthogen and dimers of amylmonothiocarbonate. The amount of xanthate catalytically decomposed increases with increasing initial concentration. Acid conditioning favors the abstraction of xanthate from aqueous solution. In any case, the absorbance of the band related to the stretching vibration of the COC groups in dixanthogen is linearly correlated to the statistical surface coverage.

Water environment and nanostructural network in a reactive powder concrete

Abstract A Reactive Powder Concrete (RPC) with an average compressive strength of 230 MPa was studied by diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS), controlled rate thermal analysis (CRTA) and low temperature nitrogen adsorption-desorption volumetry. Different water environments are observed by DRIFTS. The CRTA experiments coupled to mass spectrometric analyses allow us to differentiate various gases corresponding to adsorbed molecules and to the pyrolysis of different species. In particular the organic species added during processing can be observed. Adsorption experiments reveal a low specific surface area showing an intimate reaction between the starting components during processing. Furthermore, they show that the RPC can be considered as an open network of pores of various diameters.

Stability of the amylxanthate ion as a function of pH: Modelling and comparison with the ethylxanthate ion

Abstract The degradation kinetics of potassium amylxanthate was studied over a wide range of pH (2–12) for two cases: pure product (99.99%, molar absorptivity ϵ = 17,400 mol −1 l cm −1 ) and xanthate of technical purity (industrial reagent 65%, ϵ = 10,200 mol −1 l cm −1 ). To quantify the results, the variation with time of the absorbance (at 301 and 226 nm) of the ultraviolet spectrum of the compound was followed. Five different pH ranges in which the behaviour of the amylxanthate is different were distinguished: pH below 3.0 (D 1 ), between 3.0 and 5.0 (D 2 ), between 5.0 and 9.0 (D 3 ), between 9.0 and 10.0 (D 4 ) and above 10.0 (D 5 ). In these five, the variation with time of the absorbance was found to be in accordance with an exponential law. Thus, a relationship of the following type can be written: C=Co exp (-κT) where k = kinetic constant. The half-life ( T 1 2 ) of the compound, as well as its kinetic constant, are pH dependent and follow an exponential type law in D 2 and D 3 . They are independent of pH in D 4 and again become pH dependent in D 5 . In acidic media, decomposition products were identified as amylic alcohol and carbon disulfide. For purified amylxanthate, the relative order is found to be equal to 1 at pH = 5.0.

Interaction between finely ground pyrite and potassium amylxanthate in flotation: 1. Influence of alkaline grinding

Abstract Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Hallimond tube flotation tests, microelectrophoresis experiments and X-ray photoelectron spectroscopy (XPS) have been used to study the reactions involved in the adsorption-abstraction of K-amyl xanthate on pyrite after fine grinding in a special stainless steel laboratory rod mill. Freshly wet ground pyrite exhibits surface oxidation products which are mainly iron hydroxides or oxy-hydroxides, sulphur and iron sulphates. All these degradation products are present at the pyrite surface during the flotation process when relatively small quantities of collectors are used. For all samples prepared after grinding in basic conditions (pH between 9.0 and 12.0; regulators were NaOH and CaO), only diamyl dixanthogen was identified on the pyrite surface after flotation. Hence, dixanthogen is responsible for the hydrophobicity of the surface. It is demonstrated that in basic conditions, iron compounds and sulphoxy species are responsible for the process of oxidation of xanthate to dixanthogen.

Interaction of finely ground galena and potassium amylxanthate in relation to flotation, 3. Influence of acid and neutral grinding

Abstract Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Hallimond tube flotation and microelectrophoresis have been utilized to investigate the reactions in the adsorption-abstraction of K-amylxanthate on finely ground galena. The mineral was ground in a laboratory stainless steel rod mill under controlled conditions (pH 4.0 and 7.0) using HCl as a pH regulator. X-ray photoelectron spectroscopic (XPS) studies have been carried out in order to characterize the surface oxidation products after grinding (weak amounts of Sn and PbS2O3). The two-stage adsorption process discovered in previous studies was confirmed. For low concentrations or submonolayer capacity, the layer is formed with 1:1 monocoordinated lead xanthate and dixanthogen. For higher values of surface coverage, it is composed of lead xanthate (stoichiometric at pH 7 and non-stoichiometric at pH 4), amyldixanthogen and amylcarbonate disulphide. In the second stage mainly dixanthogen is formed. This stage corresponds to complete flotation and to a sharp decrease in zeta potentials.