Article pubs.acs.org/IECR Structural Modification of Xanthate Collectors To Enhance the Flotation Selectivity of Chalcopyrite † ‡ † † † Xin Ma, Liuyin Xia, Shuai Wang,*, Hong Zhong,*, and Hui Jia † College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, People’s Republic of China ‡ Surface Science, University of Western Ontario, London, Ontario N6G0J3, Canada *S Supporting Information ABSTRACT: A modified xanthate compound similar to xanthogen formates, S-benzoyl O-isobutyl xanthate (BIBX), was designed by introducing a carbonyl and a benzyl group into the xanthate structure. The preparation, recovery performance, and mechanism of adsorption of this compound to chalcopyrite is discussed. BIBX was synthesized using a one-pot approach with superior efficiency, which has important commercial implications. BIBX’s performance in the recovery of and mechanism of adsorption to chalcopyrite was investigated via flotation tests, adsorption quantity measurements, FTIR spectroscopy, X- ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The results show that BIBX displays a substantially stronger collecting ability toward chalcopyrite than sodium isobutyl xanthate and O-isopropyl-N- ethylthionocarbamate. Moreover, BIBX displays superior selectivity for chalcopyrite compared to pyrite. The adsorption data indicate that BIBX can be applied under slightly acidic or alkaline conditions. BIBX behaves like a bidentate ligand, bonding with the chalcopyrite copper through the thiol sulfur and carbonyl oxygen atoms. These findings are supported by FTIR and XPS data. DFT calculations predict two distinct adsorption geometries, one with one Cu atom to form a six-membered ring complex and another with two Cu atoms to form an “irregular pentagon”-shaped complex. 1. INTRODUCTION atom. In the presence of moisture, xanthates form unstable Flotation is the most common process applied in mineral xanthic acid (ROCS2H), which can be regarded as the acid separation to recover valuable minerals. In this process, the ester of dithiocarbonic acid [ROC(S)SR]. Thioamines and surface of a target mineral is rendered hydrophobic by the thioureas are xanthate- or xanthic acid (acid ester)-related compounds that arise from the reaction of an amine with attachment of a collector by chemical adsorption, van der Waals fi forces, or electrostatic bonds.1 Collectors are generally active carbon disul de. The reaction stoichiometry dictates the fi formation of dithiocarbamic acids (RNHCS2H) or thioureas toward whole mineral classes, e.g., sul de minerals, rather than 3 fi ffi [RSC(NH2)2]. toward a speci c mineral. Di culty arises when a particular fi metallic mineral must be separated from an ore with a complex Many modi ed dithiocarbamic acids (RNHCS2H) and composition or when the surface properties of the mineral thioureas [RSC(NH2)2] have been described in various patents. fl These developments have been applied in sulfide mineral result in a poor otation response. The limited resources of fl today’s mining industry increase the need to treat ores with otation. For example, O-isopropyl-N-ethylthionocarbamate fi (IPETC) was produced by the Dow Chemical Co. in 1954; lower grades, greater neness, and greater mineralogical fi fl complexity. Current practices involve the development of it proved to be selective toward copper sul de otation and more efficient collectors. copper-activated sphalerite, particularly against pyrite in alkaline ff 4−7 “Xanthate” refers to any salt with a general formula of media, as well as being e ective in acidic circuits. Alkyl ROCS M. Xanthates are currently the most important thionocarbamates were produced by Cytec (5100 series). 2 8 fl ff collectors used in the flotation of sulfide minerals and some Ackerman et al. investigated the in uence of di erent alkyl oxides, including copper, zinc, and lead oxide minerals. The first substituents (including O-alkyl and N-alkyl) on the perform- xanthate compound was discovered and named in 1823; it was ance of thionocarbamates and found that the collecting power first applied in flotation in 1924.2 Since this discovery, increases with increasing chain length of the substituents; they ff numerous other commercial alkyl xanthates have been also suggested that O-alkyl and N-alkyl substituents a ect the developed that see continued use as collectors for base-metal hydrophobicity and steric accessibility of the thionocarbamates. flotation; these xanthates include potassium amyl xanthate (PAX), sodium isopropyl xanthate (SIPX), and sodium isobutyl Received: November 25, 2016 xanthate (SIBX). From a structural viewpoint, xanthates are a Revised: May 3, 2017 product of carbonic acid, where the two oxygen atoms are Accepted: May 6, 2017 replaced by sulfur and one alkyl group replaces a hydrogen Published: May 6, 2017 © 2017 American Chemical Society 6307 DOI: 10.1021/acs.iecr.6b04566 Ind. Eng. Chem. Res. 2017, 56, 6307−6316 Industrial & Engineering Chemistry Research Article Figure 1. XRD patterns of chalcopyrite (a) and pyrite (b). In 1997, Nagaraj9,10 published a new class of thionocarbamates, 2. MATERIALS AND METHODS O-alkyl-N-allyl thionocarbamates, that were developed and fl fi 2.1. Materials and Reagents. Analytical isobutanol, widely used in the industrial otation of copper sul des and carbon disulfide, sodium hydroxide, and benzoyl chloride copper-activated zinc minerals. More recently, both exper- fi were obtained from Aladdin Industrial Co. (Shanghai, China) imental and theoretical studies on modi ed thionocarbamates and were used to synthesize the BIBX collector. Analytical and thioureas have been carried out. These structural fi methylisobutylcarbinol (MIBC) was obtained from Aladdin modi cations provided additional active points or incorporated Industrial Co. and was used as a frother in single flotation tests. functional groups on the N donor atom, resulting in xanthate- IPETC (95%), SIBX (85%), and industrial-grade pine oil ffi fl related compounds that exhibit a high a nity for oat copper frothers were purchased from Hunan Mingzhu Flotation minerals but also exhibit a high selectivity against the recovery Reagent Ltd. Co. (Zhuzhou, China). Analytical hydrochloric 6,11−14 ff 14 of pyrite. Our e orts, reported by Liu et al., involved acid and sodium hydroxide, acquired from Aladdin Industrial the introduction of a novel collector; the adsorption Co., were used for pH adjustment. Deionized water (DI water) ′ thermodynamics and kinetics of this novel collector, N,N - was used in all experiments. ′′ ‴ diisopropoxypropyl-N ,N -oxydiethylenedicarbonyl bis- The pure chalcopyrite and pyrite were obtained from the 15 (thiourea), were investigated. He et al. synthesized the Dexing Copper Mine of Jiangxi Province and the Beijing ′ novel surfactant N,N-diethyl-N -cyclohexylthiourea. They Geological Museum in China, respectively. They were crushed found that, after collector attachment, chalcopyrite exhibited manually and hand-picked. The isolated high-purity samples an unprecedented hydrophobicity that resulted in the highest were ground in a porcelain mill with agate balls to 100% recovery within the pH range from 4 to 8. passage through 74 μm. The mill discharge was subjected to an Another xanthate-based class of compounds is xanthogen ultrasonic bath, DI water rinse, filtration, and air drying, and formates, ROC(S)SC(O)OR, which were developed in the was subsequently stored in a silica gel desiccator. The chemical early 1960s. Xanthogen formates are the products from the assay (Table S1, Supporting Information) and X-ray diffraction reaction between a xanthate and ethyl chloroformates. Dialkyl (XRD; Figure 1) analysis show that the purities of the dixanthogenates are compounds with a structure similar to that chalcopyrite and pyrite were 93% and 95%, respectively. The of xanthogen formates and are the product of the reaction of minerals with a size fraction of −74 + 38 μm were used in xanthic acid with an oxidant with an ROC(S)S-S(S)COR flotation tests and adsorption measurements. The finer fraction 2 5 structure. Ackerman et al. reported that xanthogen formates (<38 μm) was used for FTIR measurements. The specific likely act as a bidentate ligand through the alkoxycarbonyl surface area of the minerals was determined by the Brunauer− − group, which likely ligates the copper atoms on the copper Emmett Teller (BET) method through N2 sorption using a sulfide surface, explaining their stronger affinity toward copper Nova1000 surface area analyzer (Quantachrome Instruments, minerals. United States). The BET surface areas of the −74 + 38 μm size Given the excellent specificity of xanthogen formates for fraction of chalcopyrite and pyrite were 0.09 and 0.11 m2·g−1, copper minerals, we modified the xanthate structure to make a respectively. new surfactant, S-benzoyl O-isobutyl xanthate (BIBX) with an The bench-scale flotation ore was from the Dexing Copper R1OC(S)SC(O)R2 structure, where R2 is a benzyl ring, to Mine, China. The valuable minerals are chalcopyrite, chalcocite, investigate the chelating ability of this structure. This pyrite, digenite, tetrahedrite, covellite, tennantite, bornite, modification introduces a carbonyl group, which forces the marcasite, molybdenite, cuprite, and malachite. The dominant xanthate collectors to function through bivalent sulfur but also gangue minerals are primarily quartz, illite, sericite, biotite, allows metal chelates to form through the thiol sulfur and carbonates, and chlorite. The multielement chemical analysis carbonyl oxygen atoms to form a