Investigation on Gold Dissolution Performance and Mechanism in Imidazolium Cyanate Ionic Liquids.

To explore green gold leaching reagents, a series of imidazolium cyanate ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium cyanate ([C2MIM][OCN]), 1-propyl-3-methyl-imidazolium cyanate ([C3MIM][OCN]) and 1-butyl-3-methyl-imidazolcyanate ([C4MIM][OCN]) were synthesized and characterized by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric (TG) analysis. In this research, the imidazolium cyanates were utilized as a solute, which not only decreased the usage of ILs but also increased their gold dissolution capability. The gold dissolution performances of three imidazolium cyanates were characterized by dynamic leaching test and Scanning Electron Microscopy (SEM). The results show that the all three imidazolium cyanates had a gold dissolution ability, and the shorter the carbon chain on the imidazole ring in imidazolium cyanate, the faster the gold dissolution rate. The gold dissolution performance of [C2MIM][OCN] was the best, and the weight loss of gold leaf was 2.9 mg/cm2 at 40 °C after 120 h dissolution in [C2MIM][OCN] mixed with 10 wt. % water. Besides this, the gold dissolution rate increased with the increase in the concentration of imidazolium cyanates as well as the reaction temperature. The gold dissolution performances of imidazolium cyanates in different solvents including water, acetonitrile, dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) were also investigated, and the weaker the polarity of the solvent, the more conducive it was to the gold dissolution reaction. The mechanism of gold dissolution by imidazolium cyanates was investigated through NMR spectroscopy and Electrospray Ionization Mass Spectrometry (ESI-MS). It was inferred that during the process of gold dissolution, Au was oxidized to Au+ and the imidazolium cations were deprotonated to form N-heterocyclic carbenes, which coordinated with gold to form gold complexes and achieve gold dissolution.

Investigation on Gold-Ligand Interaction for Complexes from Gold Leaching: A DFT Study.

Gold leaching is an important process to extract gold from ore. Conventional alkaline cyanide process and alternative nontoxic lixiviants including thiosulfate, thiourea, thiocyanate, and halogen have been widely investigated. However, density functional theory (DFT) study on the gold complexes Au(CN)2-, Au(S2O3)23-, Au[SC(NH2)2]2+, Au(SCN)2-, and AuCl2- required for discovering and designing new highly efficient and environmentally friendly gold leaching reagents is lacking, which is expected to support constructive information for the discovery and designation of new high-efficiency and environmentally friendly gold leaching reagents. In this study, the structure information, electron-transferring properties, orbital interaction, and chemical bond composition for complexes Au(CN)2-, Au(S2O3)23-, Au[SC(NH2)2]2+, Au(SCN)2-, and AuCl2- depending on charge decomposition analysis (CDA), natural bond orbital (NBO), natural resonance theory (NRT), electron localization function (ELF), and energy decomposition analysis (EDA) were performed based on DFT calculation. The results indicate that there is not only σ-donation from ligand to Au+, but also electron backdonation from Au+ to ligands, which strengthens the coordinate bond between them. Compared with Cl-, ligands CN-, S2O32-, SC(NH2)2, and SCN- have very large covalent contribution to the coordinate bond with Au+, which explains the special stability of Au-CN and Au-S bonds. The degree of covalency and bond energy in Au-ligand bonding decreases from Au(CN)2-, Au(S2O3)23-, Au[SC(NH2)2]2+, Au(SCN)2-, to AuCl2-, which interprets the stability of the five complexes: Au(CN)2- > Au(S2O3)23- > Au[SC(NH2)2]2+ > Au(SCN)2- > AuCl2-.

Combing Seeding Crystallization with Flotation for Recovery of Fluorine from Wastewater: Experimental and Molecular Simulation Studies.

For effective removal and utilization of fluorine resources from industrial wastewater, stepwise removal and recovery of fluorine were accomplished by seeding crystallization and flotation. The effects of seedings on the growth and morphology of CaF2 crystals were investigated by comparing the processes of chemical precipitation and seeding crystallization. The morphologies of the precipitates were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements. The seed crystal, fluorite, helps improve the growth of perfect CaF2 crystals. The solution and interfacial behaviors of the ions were calculated by molecular simulations. The existing perfect surface of fluorite was proven to provide the active sites for ion adhesion and formed a more ordered attachment layer than the precipitation procedure. The precipitates were then floated to recover calcium fluoride. By stepwise seeding crystallization and flotation, the products with a CaF2 purity of 64.42% can be used to replace parts of metallurgical-grade fluorite. Both removal of fluorine from wastewater and the reutilization of the fluorine resource were realized.

Effects of Hydrogen Bonds between Ethoxylated Alcohols and Sodium Oleate on Collecting Performance in Flotation of Quartz.

Hydrogen bonds play an important role in the interaction between surfactants. In this study, the effect of three different ethoxylated alcohols (OP-10, NP-10, AEO-9) on the collecting behavior of sodium oleate (NaOL) in the flotation of quartz was investigated. To explore the mechanism, the hydrogen bond between ethoxylated alcohols and NaOL was analyzed using molecular dynamics (MD) simulation. The results showed that ethoxylated alcohols promoted the collecting performance of NaOL and reduced the dosage of the activator CaO and the collector NaOL in the flotation of quartz. The Zeta potential measurement illustrated that ethoxylated alcohols promoted the adsorption of OL- on the activated quartz surface and the degree of promotion was in the order of OP-10 > NP-10 > AEO-9. The MD simulation results showed that a hydrogen bond presented between ethoxylated alcohols and OL-. Due to the hydrogen bond between the ethoxylated alcohols and OL-, the attraction force between OL- and the quartz surface increased with the addition of ethoxylated alcohols in the order of OP-10 > NP-10 > AEO-9 based on the MD simulation results. As the result, the addition of ethoxylated alcohols increased the adsorption density of OL- on the activated quartz surface, which explained the promotion of the collecting performance of OL- in the flotation of quartz.

Assembling reduced graphene oxide hydrogel with controlled porous structures using cationic and anionic surfactants.

The roles of cationic and anionic surfactants in assembling reduced graphene oxide hydrogels (RGOHs) and controlling their porous structures are studied in this work. The mechanisms of the surfactant effects were studied by x-ray diffraction, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and electrochemical methods. The morphology and structure of graphene oxide and RGOH were examined by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The experimental results showed that surfactants could modify the structure of as-prepared RGOH but did not change the chemical or physical properties of the reduced graphene oxide (RGO) sheets. The modification was achieved by changing the orientation of graphene oxide sheets in aqueous solutions. It was also found that RGOH could not be prepared in the presence of high dosages of cationic surfactant because the RGO sheets were stacked piecewise with just one orientation and could not be cross-linked at any angle. The presence of an anionic surfactant did not affect the formation of RGOH but only enlarged the pores in its cross-linking structure. In addition, RGOHs prepared with anionic surfactants were found to have a higher specific capacitance compared to RGOHs prepared with cationic surfactants.

Selective gold extraction from electronic waste using high-temperature-synthesized reagents.

For over two hundred years, cyanide has served as the primary reagent for gold extraction. However, due to its high toxicity, the use of cyanide poses significant risks. Traditional low-toxicity leaching reagents have limitations that restrict their widespread industrial application, leading to the necessity for the development of new, efficient, and low-toxic gold leaching reagents to support sustainable gold production. In this study, a novel, efficient, and low-toxicity gold extraction reagent was synthesized at high temperatures by combining urea, sodium carbonate, and a specific iron salt. The research delved into the leaching ability of the reagent under different synthesis conditions and examined the generation of free cyanide content as a by-product. Findings indicated that reagents synthesized with either potassium ferrocyanide or potassium ferricyanide displayed comparable leaching capabilities. Reagents synthesized at 800 °C exhibited lower levels of free cyanide ions and reduced toxicity. Additionally, this reagent demonstrated exceptional selectivity for gold, while in minimal dissolution of copper, iron, nickel, lead, and iron from computer central processing unit (CPU) pins. Under optimal conditions, the efficiency of gold extraction from CPU pins reached 94.65%. Hence, this reagent holds significant potential for the low-toxicity extraction of gold from electronic waste or auriferous concentrates.

Aggregation mechanism of colloidal kaolinite in aqueous solutions with electrolyte and surfactants.

In this study, the effect of surfactants and electrolytes on stability of kaolinite dispersions was analyzed by measuring suspension transmittance, zeta potential, and adsorption. It was experimentally found that the compression of kaolinite electric double layer caused by NaCl addition may reduce the electrostatic repulse force to facilitate the aggregation of kaolinite particles. Surfactant facilitate the aggregation of kaolinite particles mainly through the adsorption of it on the surface of kaolinite to generate hydrophobic force. Compared to anionic surfactant, the cationic surfactant has a better flocculation effect because it can be used in a wide pH range and its adsorption can reduce the electrostatic repulse force between kaolinite particles.

Selective and efficient adsorption of Au (III) in aqueous solution by Zr-based metal-organic frameworks (MOFs): An unconventional way for gold recycling.

Recycling precious metals from secondary resources is of great environmental and economic significance. In this study, the Zr-based MOFs UiO-66-NH2 was synthesized and used to adsorb Au (III) in aqueous solution. The ultrafine particle size (∼50 nm), excellent crystallinity and huge specific surface area (1039.2 m2 ·g-1) were verified by transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and surface area analysis. About 50 % Au (III) was adsorbed within 6 min and the maximum adsorption capacity at 298 K reached up to 650 mg·g-1, showing superiority to traditional adsorbents. The general order kinetics model and Liu equation were suitable to describe the adsorption process, which was spontaneous, endothermic and driven by the increasing system entropy. Electrostatic attraction between -NH3+ and Au (III) anions and inner complexation to Zr-OH played a vital role in adsorption. Au (Ⅲ) was reduced to Au° by amino groups via redox reaction certified by X-ray photoelectron spectroscopy (XPS), PXRD and high-resolution transmission electron microscopy (HRTEM) analysis. Moreover, UiO-66-NH2 displayed high selectivity, robust stability and excellent reusability, making it an ideal candidate for gold recycling in industrial practice.