V. A. Chanturiya, I N. Matveyeva, I A. Ivanova, N. K. Gromova
institute of Complex Exploitation of Mineral Resources (IPKON), RussianAcademy of Sciences, Moscow, Russia
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ABSTRACT
In Pt- and Au-keeping complex ores processing, about 10% 15% of noble metals are lost with true tailings that are due to low floatability of Pt- and Au-keeping minerals by the conventional collectors, With the aim to achieve the effective recovery of noble metals at flotation of Pt-Cu-Ni and Au-keeping ores organic complex reagents keeping electron-donating atoms of nitrogen, oxygen, sulfur or phosphorus may be offered as selective collectors for the indicated minerals. These reagents tend to form complex compounds with PGM. Besides this, Cu-Ni-Pt and complex Pt and Au carbonated mica ores are characterized by finely disseminated (up to nanometer size) mineral forms of Pt in multivalent states. In this connection, the use of a combination of the strong ionic collectors with nonionic reactants that are capable to derivate complex compounds with multivalent PGM seems to be expedient for this type of ores.
In the research new complex reactants were tested such as cyclic alkylene-trithiocarbonates, oxyalkyl butylxanthogen acid ethers, a combination of the collectors — mercaptobenzothiazole (MBT) and dialkyldithiophosphates (DTP). Sorption and flotation tests were made with monomineralic samples of chalcopyrite, pentlandite, pyrrhotite, pyrite, and Pt-Cu-Ni sulfide ore samples. Sorption properties were examined by the extraetive UV spectrophotometric method and potentiometric measurements.
To indicate a structure of modified xanthate solutions the method of a thin-layer chromatography (TLC) was applied. The chromatographic behavior of the basic components of modified xanthate solution -- ButX, cyclic propylene-trithiocarbonate (PTTC), diethyl-dithiocarbamate (DEDC) and the product of its modification — oxypropyl-S-ether of dithiocarbamatic acid was studied on plates “Silufol UV — 254”. The composition of organic solvents and its ratio in a mobile phase was determined for simultaneous chromatography of the main components of a reaction mixture.
It was found that operating selectivity of MBT, DTP and cyclic alkylene-trithiocarbonates incorporated in modified xanthate in relation to Pt-Cu-Ni and Au-containing sulfide minerals might be explained by an electoral sorption of this nonionic collector on a surface of the minerals studied. It was demonstrated that the application new reagent modes with the use of a combination of designed complex reactants helped to increase the extraction index of Pt- and Au-keeping minerals from complicated ores.
Keywords: Complex-forming reactants; Cyclic propylene-trithiocarbonate; Oxypropyl-S-ether; Sorption; Flotation; Pt-Cu-Ni and Au-keeping minerals
INTRODUCTION
In Pt-Cu-Ni rich and low-sulfide ores processing, approximately 10% ~15% of precious metal components are lost with waste tailings primarily due to low floatability of platinum group minerals with conventional collectors. The problem of improving the quality of con- and decreasing the losses of precious metals with wastes can be solved by developing new effective collectors on the basis of complex-forming reagents.
In the Institute of Complex Exploitation of Mineral Resources (IPKON) Russian Academy of Sciences researches on development of new flotation reactants, selective to platinum group metal (PGM) and Au due to formation of almost insoluble complex compounds are carried out. Such reagents as alkylene-trithiocarbonates, incorporated in modified xantgate solution, mercaptobenzothiazole and dithiophosphate were offered to enhance xanthate selectivity with respect to PGM-bearing sulfides. It has been found that the alkylene-trithiocarbonates incorporated in modified xanthate are selectively adsorbed on the surfaces of Cu-Ni-Pt and Au-bearing sulfides, thus increasing the floatability of these minerals with xanthate (Matveyeva et al., 2006). New reagent modes involving a combination of designed complex- forming collectors provides an increase in PGM and Au recovery from complex ores as compared to that obtained in flotation with xanthate alone (Chanturiya et al., 2006).
A significant advantage of the solution modification mode as compared to using combinations of completed reagents consists in the possibility of controlling the composition of the solution and obviating the necessity of dissolving the substances resistant to dissolution before feeding them into the pulp.
In developing this solution modification mode for new selection reagents design it was expedient to study the flotation and sorption properties of diethyl-dithiocarbamate (DEDC), modified by propylene chlorohydrin or propylene oxide. As a result of the reaction S-ethers are formed. These compounds are known as non-ionic reagents providing a positive effect at flotation of sulphidic ores, due to formation of coordinated band between nitrogen and sulfur atoms, on one hand, and non-ferrous and precious metals ions, on the other.
Depending on length of a hydrocarbonic radical and the assistant, S-ethers can show various flotation properties. Derivatives of dialkyl-dithiocarbamate, having hydrophilic assistants (hydroxyl-, carboxyl-, sulfate-group, etc.) incorporated into dithiocarbamate group are used by Coal Industry Ltd. (GB) as depressors of pyrite at coal flotation. Dow Chemical Company and Cyanamid (USA) developed reagents that are complex S-ethers of di-thiocarbamatie acid and applied at flotation of sulfides of copper-nickel ores. In Russia reagent DECE (analogue of Chinese reagent CID) is synthesized and it is applied for extraction of copper and molybdenum sulfides.
2-Mercaptobenzothiazole C7H4SNSH (MBT) is a heterocyclic nitrogen-bearing compound which is used in analytical chemistry as a reactant for gravimetric and spectrophotometric determination of platinum group metals (PGM). Pt(C7H4S2N)4 formed is a slightly soluble compound with a structure is one of the inner-complex compounds. Pt(C7H4S2N)4 is dissolved in chloroform and it has a band of absorption with a maximum at 300 nm (ε = 32500). This characteristic maximum is used for spectrophotometric definition of Pt (IV). MBT is also applied for extractive separation of PGM (KirkOthmer, 1980). The salts of dialkyl-di-thiophosphorous acids (DTP), i.e. (C2H50)2PSSH may derivate inner-complex compounds with a number of platinum metals as well. The DTP salts are more selective than xanthates and quantitatively precipitate Pt from neutral and acidic solutions (Gizburg et al., 1 973).
As a collector MBT is produced by Cyanamid (USA) under the mark R Aero-404 and is applied at flotation of oxidized Pb and Cu minerals, free thin Au, Cu-Zn and Cu-Mo ores (Shubov et al., 1990). Clariant (Germany) produces Hostaflot M-91 that is a mixture of MBT and DTP. It is recommended for the flotation of Cu minerals, noble metals, and also Au, associated with pyrite.
Dialkyldithiophosphates (DTP) with different length and frame of hydrocarbon radical are produced by Cyanamid (USA), Clariant (Germany) and some other companies and are used at flotation of Cu, Pt-Cu-Ni and Au ores as separately, and in a combination to xanthate.
The objective of the work presented in this paper was to give the experimental substantiation for the mechanism of interaction between special reagents that may form complex compounds with noble metals incorporated in sulfide minerals on the basis of new data about sorption and flotation properties of selective collectors. In addition, efficiency of joint application of non-ionic and ionic collectors was studied with the aim to achieve the maximal extraction of sulfides from rich and low-sulfide ores.
Taking the above challenges into account, the following parameters were studied:
• conditions under which selective collectors form complex compounds with precious metals at flotation processing;
• sorption values of mercaptobenzothiazole (MBT) and its mixes with dithiophosphate on Pt-Cu-Ni minerals and pyrrhotite;
• changes in potential values of Au-containing pyrite mineral electrode;
• collective properties of complex-forming reagents at monomineralic flotation and ore flotation tests that were carried on the samples selected from Pt-Cu-Ni and Au-pyrite ores.
EXPERIMENTAL
The characteristics of sorption of new collector reagents on sulfide minerals of Cu-Ni-Pt ores, ionic-molecular composition of mineral suspensions and surface properties of sulfides were examined by the extraction UV spectrophotometric method, with potentiometric tests and thin-layer chromatography also involved. Flotation tests were made with monomineralic samples, mineral mixtures and Cu-Ni-Pt ore samples. The chemical composition of the samples is shown in Table 1.
The formation of complex compounds of cyclic alkylene-trithiocarbonates (PTTC), incorporated in modified xanthate, with Pt, Au, Fe and Cu salts in aqua and aqua-ethanol solutions was studied by extractive specrtophotometry and chromatography. The following salts were used: H2[PtCl6], H2[AuCl6], CuSO4, FeCl3 and FeSO4.
H2[PtCl6], that itself is a complex compound, enters reactions of legand exchange, possesses oxidizing properties and may act as a strong acid. H2[PtCl6] is rather inert kinetically. With the aim to increase the speed of legand exchange such reducing agents as glucose, an ascorbic acid or SnCl2 are applied.
It is noteworthy that in aqueous solution [PtCl6]2 reveals adsorption maximum at the wavelengths 257 nm (ε = 2.45 x104), 262 nm(ε = 490), 353 nm(ε = 50), 453 nm, 266 nm and 239 nm. UV-spectrophotometric method applied doesn’t make it possible to identify Pt:PTTC and Au:PTTC complexes because both initial (H2[PtCl6] and H2[AuCl6]) and newly formed (Pt:PTTC and Au:PTTC) compounds adsorbed light in the same range of spectrum.
Greater sensitivity of a method of thin-layer chromatography (TLC) and simplicity of compounds identification by TLC-analysis has allowed to analyze components studied in a low-concentrated solution and in a firm condition. The analysis is based on various chromatographic mobility of both of the complexes — [PtCl6]2- and Pt:PTTC. Investigated compound was dissolved in organic solvents or extracted from a water solution into tetra-chloride carbon. A solution was put by capillary onto chromatographic plate (UV-254) and then it was aluated by specially picked up mixture of organic solvents. Indicated components were identified by their own color on a plate after it was gried and display in iodine.
RESULTS AND DISCUSSION
TLC and UVS analysis of PTTC compounds in solution
TLC-analysis of components of PTTC solution in H2[PtCI6] has allowed to define complex connections forming in it. Three-component elluated mix or a so-called mobile phase (MP), containing polar and non-polar solvents: acetone, benzole and dioxan at a parity (4:2:4), has allowed to divide components on a plate and to shift complex Pt:PTTC = 1:2 from a line of start (Table 2). On chromatogram three spots have appeared that testified a simultaneous presence of H2[PtCl6], chloro- and aqua-complexes of platinum in mix solution.
At a contact with PTTC after eluating, drying and displaying on a plate have appeared four spots, three of them correspond to H2[PtCl6], and the spot, described by greater Rƒ = 0.81 obviously corresponds to complex Pt:PTTC In addition, residual PTTC in a complex solution can be identified in a mix: acetone : benzole : tetra-chbride carbon (2:3:6) by own color of a spot with Rƒ = 0.5.
PTTC interaction with Fe2+ and Fe3+ ions at varying pH doesn’t reveal change in color of a solution or occurrence of a deposit.
It is shown that after PTTC contact with Cu2+ in an interval of pH 5~l2 the viscous red-orange substance is formed.
Red-orange color appears practically immediately after draining of components and is stable for a long time. In water environment PTTC cooperates with Cu2+ only at presence of chloride-ions. As it has appeared, besides the chloride-ions, the colored compound can be formed at presence of sulfide-, hydrosulfide-ions and elementary sulfur.
Once a Cu+ salt solution (pH 5-9) comes into contact with PTTC, formation of red-orange compound is observed. UV-spectra of absorption of dioxin and aqua-dioxan solutions (0.2:5) show two maxima of absorption: the first coincides with maximum of PTTC (319 nm). The second maximum at 280 nm most likely corresponds to a strip of a charge moving in a molecule of complex compound. Optimum conditions for complex formation are found on curves of saturation, they are reached at Cu:PTTC:Cl = 1:1:2,
To summarize, the results of chromatographic and spectophotometrie analysis proved
that cyclic alkylene-trithiocarbonates incorporated into modified xanthate solution, form stable color compounds with Pt and Cu ions at flotation conditions and help increase PGM extraction into flotation concentrate.
UVS analysis of OPEDEDC in modifying procedure
When modif\jing diethyl-dithiocarbamate (DEDC) with alkylene chlorohydrins, in particular, propylene chlorohydrin or propylene oxide in the water enviroment without heating 2-oxypropyle ether of diethyl-dithiocarbamate acid (OPEDEDC) is formed. The general formula of 2-oxyalkyl ethers of dialkyl- dithiocarbamate acid is the following:
R2N-CS-S-CH2-CH-R’
∣
OH, where R and R’= H, CH3,
C2H5
S-ethers analyzed are non-ionic compounds that possess various chemical and sorption properties depending on the length of the hydrocarbon radical.
Preliminary tests were done to form and extract 2-oxypropyle ether of diethyl- N, N—dithiocarbamate acid (OPEDEDC). OPEDEDC is oiler, viscous, pale yellow liquid well soluble in organic solvents, but with low solubility in water (<0.5 g/L). This compound is steady at storage.
UV-spectra of OPEDEDC have characteristic maxima of absorption at 256 nm and 275 nm (in water), 250 nm and 280 nm (in ethanol), 285 nm and 259 nm in tetra-chloride carbon and 281 nm in benzene. It is established, that OPE]JEDC is also one of the complex-forming reactants in relation to Cu, Mo and some precious metals (Pt), possessing flotation activity. However, low solubility of such a compound in water essentially complicates their introduction into flotation process.
With the aim to obviate the necessity of dissolving the ethers resistant to dissolution before feeding them into the pulp, they were formed in low-concentrated aqua solutions by modifying diethyl-dithiocarbamate by with alkylene chiorohydrins, in particular, propylene chlorohydrin at the ration 1:0.9 - 1:1.4 of the main components (Chanturiya, 2005). In the procedure decrease in DEDC concentration and formation of a new compound — OPEDEDC was observed. High speed of the reaction and complex-forming properties of compounds studied in connection to noble metals makes it promising to test OPEDEDC as an additional collector at flotation of sulfide minerals, containing noble metals.
OPEDEDC sorption and flotation tests on Pt-Cu-Ni and pyrrliotite samples
Sorption characteristics of OPEDEDC from the modified solution and its mixture with ButX have been studied on the samples of pyrrhotite and Pt-Cu-Ni. UV-spectrum of aqua solution of OPEDEDC has characteristic maxima of adsorption at wavelength of 272 nm and 256 nm, In a mixture of collectors — OPEDEDC and ButX, ButX may be identified at 301 nm as optical density of OPEDEDC solution at 301 nm is close to zero. it can be seen in Fig. 1, that in a liquid phase of Pn-Po suspension there is a decrease of optical density at 272 nm from 1 .18 (curve 3) up to 0.97 (curve 1), that testifies a decrease of OPEDEDC concentration from 21.1 mg/L up to 17.45 mg/L. The value of OPEDEDC adsorption OPDEDTK on a mineral surface was calculated as 0.073 mg/g or 17.3% of initial amount of the reagent. At contact with Po (curve 2) the reduction of optical density is insignificant, OPEDEDC adsorption on does not exceed 1% of its initial dosage. Thus, selective adsorption of OPEDEDC on Pt-Cu-Ni sample is observed.
In addition, OPEDEDC adsorption tests on Pt-Cu-Ni sample from a mixture of collectors have shown that in case of joint presence of reagents OPEDEDC adsorption on a mineral surface increases in comparison with application of OPEDEDC alone. Thus, full absorption of ButX from a solution is observed. To summarize the results of sorption experiments, the modified collector OPEDEDC selectively adsorbs on a surface of Pt-containing Cu-Ni sulfides, and It is noteworthy that OPEDEDC adsorption from ButX solution is higher, than from a solution of OPEDEDC alone.
Experiments on flotation of Pn-Po sample revealed that OPEDEDC at its dosage of 160 g/t helps to receive a higher yield of a concentrate (60%) in comparison with ButX (48.4%), and it doesn’t grow more with an increase in collector dosage up to 240 g/t (Fig. 2). A mixture of collectors — 160 g/t OPEDEDC and 100g/t ButX helps to enhance mineral floatability up to 78.6%, that is by 18.6% higher, than at OPDEDTK alone and by 30.2% — in comparison with ButX. Thus, the efficiency of OPEDEDC application as additional collector for Pt-Cu-Ni minerals flotation improvement is evident.
Hostaflot M-91 sorption and flotation tests on Pt-Cu-Ni and pyrrhotite samples
UV-spectrum of Hostaflot M-9 1 solution has the characteristic maxima of absorption at 318 nm, 229 nm and 203 nm, coinciding 2-Merca- ptobenzothiazole C7H4SNSH (MBT) (Lomakina and Yakovskaya, 1969). Concentration of Host- allot M-91 was determined by light adsortion at wavelength of 318 nm, as dithiophosphate (DTP) doesn’t adsorbed light in this part of a spectrum.
As a result of experiments the adsorption curves of Hostaflot M - 91 for all studied mm- era! samples were obtained. The adsorption values of Hostaflot M - 91 on minerals grows with an increase in its concentration up to 50 mg/L and reaches 0.88 mg/L on pentlandite-pyrrhotite and 0.62 mg/L on chalcopyrite that makes accordingly 88% and 62% from its initial quantity. Reagent adsorption on both samples of pyrrhotite doesn’t exceed 15 (II) or 29% (1) depending on the impurities content.
In addition, Fig. 3 shows the comparison adsorption of collectors — ButX, Hostaflot M-91 and (DTP) on pyrrhotite (1), at the initial concentration of the reagents 50 mg/L. Diagram follows that the greatest value of a sorption — 52% is characteristic for ButX and the least value is demonstrated by DTP 11%. Hostaflot M-9 1 takes an intermediate position (32%) between ButX and DTP due to MBT incorporated in its combination.
Experiments on Pn-Po sample sorption revealed that 100% of the initial amount of xanthate was adsorbed on the mineral surface, while Hostafolt M-9 1 and DTP sorption is nearly 88% and 82%, correspondently. The small decrease in sorption ability of this sample in relation to Hostafolt M-91 and DTP is explained by lower sorption of the reagents on pyrrhotite, which is incorporated into Pn-Po sample.
Thus, Hostaflot M-91, entering complex- forming agents as MBT and DTP is more selective collector for Pt-Cu-Ni sulfide minerals than ButX. Low sorption of these reagents on pyrrhotite samples in comparison with ButX or its entire absence is the basis for use them at selective flotation of Pt-Cu-Ni sulfide minerals.
Flotation tests performed on Pn-Po sample have shown that the greatest yield of a concentrate (57 %) is achieved by ButX as the collector at the dosages of 100-450 g/t (Fig. 4). The analog dosages of Hostaflot M-9 1 produced not more than 50% output, and DTP — about 40%. The decrease in Pn-Po floatability by Hostaflot M-91 and DTP can be explained by low flotation activity of pyrrhotite presented in this sample.
Potential measurements of Au-containing pyrite mineral electrode
Finely, the changes in Au-containing pyrite potential as a function of complex-forming collectors were studied. Potential-concentration curves of pyrite mineral electrode reflected maximal influence of ButX ions. At 25 mg/L ButX concentration mineral electrode changed its positive charge (+105 my) into negative values and reached —70 mV at 100 mg/L that testified about active ButX adsorption on a stir- face.
Sharp decrease in potential values at growing concentration of the collector can be explained by rapid oxidation of pyrite surface and ButX adsorption. Under conditions studied the saturation of adsorbed layer on the mineral surf ace was not entirely reached.
Modified ButX strongly lowered pyrite potential, too, but as compared to common ButX potential values were a little bit positive (by 10—20 mV in dependence of reagent concentration), that can be explained by non-ionic complex-forming reactant — PTTC, entered solution.
Hostaflot M-9l, as a mix of MBT and DTP, affected pyrite potential but in a narrower interval(+105 ~+30 mW) that can be revealed in its greater selectivity in comparison with ButX at flotation of Au-pyrite complex ores.
CONCLUSIONS
As a result of studied presented in the paper, the new complex reactants, involving modified solutions have been developed and a combination of an ionized collector (ButX, DlP) and a non-ionized one (PTTC, OPEDEDC, MBT) for effective Cu-Ni-Pt and Au minerals flotation has been substantiated.
With an application of Uv extractive spectrophotometry and thin-layer chromatography methods there have been determined, that under flotation conditions cyclic PTTC, incorporated into modified BuX solutions, tended to form steady color compounds with fl Au and Cu.
The conditions for modifying DEDC by propylene chlorohydrins, resulted in organic ether OPEDEDC formation, have been developed. It has been found that OPEDEDC incorporated in modified collector solution was selectively adsorbed on the surfaces of Cu-Ni-Pt sulfides, thus increasing the floatability of these minerals with xanthate. New data on sorption and flotation activity of the components of modified xanthate and dithiocarbamate solutions with respect to CU-NI-PT sulfide minerals have been obtained.
It has been determined that complex reactant Hostaflot M-9l has revealed electoral sorption on Pt-Cu-Ni sulfide minerals and helped to enhance selectivity of Pt-Cu-Ni and Au ores flotation.
Acknowledgements Financial support fitm Grant of the President of Russian Federation “Scientific School of academician V. A. Chanturiya” NSb 2098.2008.5 and Grant RFFI 08-05-00244 is highly acknowledged.
REFERENCES
Chanturiya V. A., Ivanova t A. and Tyurnikova V. L, 2005. Modifring of flotation reactants solutions by highly active chemicaLs. Proceedings of the 5’ Congress of Mineral Processing Engineers (Russia and CIS-countries), Moscoç Russia
Chanturiya V. A., Nedosekina T. V. Matveyeva t N. and Ivanova ‘It A., 2006. New reagents and reagent modes for flotation of Cu-Ni-Pt ores of Russia Proceedings. of the 23’ IMPC, Istanbul, Turkey.
Ginzburg 5.1. Ezerskaya N. A., Prokof’eva L V., Fedorenko N. V. Shenskaya V. I. and Belskiy N. IC., 1973. Analytical chemistry of platinum metals. Moscow [in Russian].
Kirk-Othmer encyclopedia, 1982. 3d ed., v20, New York
Lomakina L. N. and Yakovskaya B. K., 1969. Detennination of solubility and constant of acid dissociation of 2-Mercapto- benzothiazole. Vesmik of Moscow University, 5. [in Ibis- sian].
Matveyeva it N., Ivanova it A. and (Jromova N. K., 2006. Study of cyclic alkylene-trithiocarbonates sorption on Pt- beating minerals at flotation. Proceedings of the 10’ Conference on Environment and Mineral Processing, Part 1, VSB-flI Ostrava, Czech Republic.
Shubov LYa et al. Flotation reagents in mineral processing treatment, booki, M, Nedra, 1990, p.82, 138 [in Russian].
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