Ionic liquids functionalized chitosan: An effective, rapid and green adsorbent for gold recovery.

Thiosulfate has been considered as a more environmentally-friendly alternative to cyanide salts for the extraction of gold from gold ores and the development of affordable, green and efficient adsorbents for the isolation of gold-thiosulfate complex (Au(S2O3)23-) from the leaching solution remains a significant challenge. To address this issue, chitosan, a natural macromolecule, was selected as a carrier and chemically modified with ionic liquids. The ionic liquids modified chitosan showed greater adsorption capacity towards Au(S2O3)23- compared with pristine chitosan. The adsorption of Au(S2O3)23- on ionic liquid modified chitosan followed Freundlich isotherm and pseudo-second order kinetic models, involving an anion-exchange mechanism with liquid film diffusion as the rate-limiting step. The chitosan modified with butylimidazolium-based ionic liquid had an adsorption capacity of 5.0 mg g-1 for gold (10 mg L-1 of gold, pH 6, 2 g L-1 of adsorbent dosage), outperforming other reported adsorbents. The ionic liquid modified chitosan showed a high adsorption efficiency of up to 96.7 % for Au(S2O3)23- in an actual thiosulfate leaching solution with a desorption efficiency of 98.4 %, suggesting that the ionic liquid modified chitosan has the potential to be a eco-friendly, biocompatible and effective adsorbent for the recovery of Au(S2O3)23-.

Efficient removal of heavy metal and antibiotics from wastewater by phosphate-modified hydrochar.

The preparation, characterization and adsorption performance of the phosphate-modified hydrochar (P-hydrochar) for Pb(II) and ciprofloxacin removal are investigated. Pb(II) and ciprofloxacin adsorption behavior fit well with the Hill model with the adsorption capacity of 119.61 and 98.38 mg/g, respectively. Pb(II) and ciprofloxacin adsorption kinetic process are accurately described by the Pseudo-second-order. Pb(II) and ciprofloxacin have synergy in the binary contaminant system, which reveals that Pb(II) adsorption amount is augmented. While ciprofloxacin adsorption amount is also augmented at low Pb(II) concentration and hindered at high Pb(II) concentration. Pb(II) adsorption mechanisms on P-hydrochar (e.g. precipitation, π-π interaction and complexation) are different from the ciprofloxacin (e.g. hydrogen bonding, pore filling, electrostatic attraction). Pb(II) and ciprofloxacin adsorption process are further analyzed by the density functional theory. The coexisted ions have little influenced on Pb(II) and ciprofloxacin adsorption. P-hydrochar still has large Pb(II) and ciprofloxacin adsorption capacity after five cycles. This result indicates that poplar sawdust waste can be converted into an efficient adsorbent to remove Pb(II) and ciprofloxacin from wastewater,.

Preparation of valuable pyrolysis products from poplar waste under different temperatures by pyrolysis: Evaluation of pyrolysis products.

Poplar waste is used as feedstock to prepare valuable pyrolysis products by pyrolysis under different temperature. The bio-oil is rich in aldehyde with the maximum relative content of 47.15%, which has potential application in chemical industries. Pyrolysis temperature has significantly influenced the composition and heating value of bio-gas. The maximum heating value of bio-gas is 14.56 MJ/Nm3. Biochar is used as an adsorbent to adsorb Ag+ from aqueous solution with the adsorption capacity of 76.09 mg/g. Biochar forms the value-added Ag-Biochar composite by reduction after adsorption Ag+. While, Ag-Biochar composite can be used as catalyst for methyl orange removal with the maximum removal of 94.08%. Ag-Biochar composite is also used as lithium ion battery cathode material for energy storage with the specific capacity of 345 mAh/g. Besides, preliminary economic analysis is used to evaluate the economics of pyrolysis process with the total annual revenue of $115, 725/year.

Analysis of Highly Efficient Adsorption of Au(S2O3)2 3- by Calcined Cu/Fe Layered Double Hydroxides.

One of the main problems affecting the application of gold thiosulfate leaching is the difficulty in recovering gold from the leaching solution. Our previous studies revealed that when using calcined Mg/Al layered double hydroxides (LDHs), the single adsorption capacity of Au(S2O3)2 3- can reach 7.76 mg/g. In order to further examine the recovery of Au(S2O3)2 3- by various types of LDHs, the divalent metal and trivalent metal ions in LDHs were altered. Also, thiosulfate anions are introduced between the layers of LDHs to reduce the competitive adsorption of thiosulfate ions in the solution. Results show that the calcined LDHs (CLDH) prepared with Cu/Fe-LDHs are the best at adsorbing Au(S2O3)2 3-. Compared with Mg/Al-CLDH, the single adsorption capacity reaches 48.6 mg/g. The pseudo-second-order kinetic model is more suitable for describing the adsorption of Au(S2O3)2 3- by Cu/Fe-CLDH. The adsorption isotherm fitting experiment indicates that the adsorption by Cu/Fe-CLDH of Au(S2O3)2 3- conforms to the Langmuir model. During the process of Cu/Fe-CLDH adsorbing Au(S2O3)2 3-, CLDH restored part of the layered structure, and Au(S2O3)2 3- was inserted between the layers as a counteranion. Furthermore, the reduction of Au(S2O3)2 3- by low-valent iron compounds in the adsorbent promoted the process of Cu/Fe-CLDH adsorbing Au(S2O3)2 3-.

Micromechanism Study of Strengthening Effect of Copper on Gold Thiosulfate Leaching.

To study the effect of copper on gold thiosulfate leaching, the gold dissolution of three different sample powders (gold, gold/copper, and gold/copper oxide) in a solution of 5 mM Cu2+, 0.4 M ammonia, and 0.1 M thiosulfate was studied. Scanning electron microscopy analysis showed no sulfur passivation on the gold surface, and there were more prominent corrosion pits on the gold surfaces of samples that were ground with copper or copper oxide. The Evans diagrams showed that copper and copper oxide can promote both the anode and cathode processes of gold dissolution. Based on first principle simulations, copper and copper oxide exhibited the ability to disrupt the stability of gold surface atoms and cause different degrees of relaxation. Both copper and copper oxide reduce the d-band center of the gold surface atoms and the adsorption between gold and thiosulfate. In addition, the bond length of the S-S bond of thiosulfate adsorbed onto the gold surface was longer when copper or copper oxide were not present. According to the change in the potential surface energy, the energy barriers for gold atom dissolution from gold, gold/copper, and gold/copper oxide surfaces were 1.79, 0.72, and 1.01 eV, respectively.