M. Kongolo

Environmental desulphurization of four Canadian mine tailings using froth flotation

Abstract Environmental desulphurization is an attractive alternative for management of acid generating tailings. This process placed at the end of the primary process treatment circuit will reduce a large amount of the problematic tailings by concentrating the sulphide fraction. To produce desulphurized tailings, non-selective froth flotation is the most adapted method. The desulphurization level is fixed by the sulphide content of the tailings and their neutralization potential (NP). The final residue should have enough NP to safely compensate for its acidity potential (AP). In this paper, the authors present the results of a battery of tests conducted in Denver cells to study the sulphide flotation kinetics of four different mine tailings samples which contain 2.9 S%, 3.4 S%, 16.2 S% and 24.2 S%, respectively. Tailings P, M, and G are cyanide free and can be floated at pH values of less than 10 by using amyl xanthate as the collector agent. However, tailings D, which come from a gold cyanidation process, did not provide good sulphide recovery because of pyrite depression (even after cyanide elimination followed by a sulphide surface activation and a pH decrease). To successfully overcome this problem, amine acetate was used. This collector allows easy flotation without a pretreatment stage. Dosage of the two type of collector were optimized for the tailings studied. The results of all kinetic tests and collector dosage optimization were combined to establish a model which will estimate the cost of desulphurization. A preliminary analysis shows that the expense of the implementation of this desulphurization technology is comparable to other rehabilitation methods.

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.

Physico-chemical properties of tailing slurries during environmental desulphurization by froth flotation

Abstract Environmental desulphurization has been established as an alternative solution to control acid mine drainage due to the reactivity of sulphide tailings when exposed to open air conditions. In fact, this process placed at the end of the primary treatment circuit greatly reduces the amount of problem tailings by concentrating the sulphide fraction. An acceptable target for sulphide content can be estimated from the acidity potential (AP), neutralization potential (NP) and the net neutralization potential (NNP) of the mill tailings. To produce desulphurized tailings, non-selective froth flotation is the most common method used in previous work. In this paper, the authors have focused the physicochemical properties of the pulp as the main parameters affecting the non-selective sulphide flotation. The pyrite depression due to lime addition during the former process represents the main problem. Several laboratory tests were conducted using a Denver cell to choose the best and most economical collector. Other tests were done to select the best frothing agent. The pH and redox potentials were investigated as parameters of great importance in flotation performance. For studying the sulphide flotation kinetics, two mine tailings are chosen which are characterized by a weak neutralization potential (under 37 kg CaCO3/t). Tailings S and L are cyanide free and contain respectively 5.27 and 10 wt.% sulphur. Collector dosage was optimized for these tailings as well as the flotation time and the results show that tailings L needed more collector than tailings S. Desulphurization costs were estimated to be CND

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

0.35 per ton (dry tailings), which is very comparable and competitive to existing method for tailings management.

Chemical surface modifications of sulphide minerals after comminution

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.

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

Abstract The superficial chemical heterogeneity of sulphide minerals can be natural or induced. Comminution is one possible way for changing, sometimes drastically, the surface state of sulphides, which, consequently, modifies the reactivity of the divided solid. Using different investigation techniques at the molecular scale, the chemical nature of the surface of galena, pyrite, chalcopyrite and sphalerite after various comminution conditions can be precisely described. Galena and pyrite are partially covered with piles of oxidized sulphates and carbonates species. Elemental sulfur was also revealed in variable amounts. After wet grinding, the chalcopyrite surface is altered by the formation of a continuous 200-nm-thick layer iron oxy-hydroxides. Xanthate molecules can be used as molecular probes for describing the surface of ZnS after wet grinding.

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

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.

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

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 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 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.

The comparison between amine thioacetate and amyl xanthate collector performances for pyrite flotation and its application to tailings desulphurization

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.