Optimization of process parameters using response surface methodology for Pd(II) extraction with quaternary ammonium salt from chloride medium: kinetic and thermodynamics study

Adsorption and desorption processes of toxic heavy metals, regeneration and reusability of spent adsorbents: Economic and environmental sustainability approach

A growing number of variables, including rising population, water scarcity, growth in the economy, and the existence of harmful heavy metals in the water supply, are contributing to the increased demand for wastewater treatment on a global scale. One of the innovative water treatment technologies is the adsorptive removal of heavy metals through the application of natural and engineered adsorbents. However, adsorption currently has setbacks that prevent its wider application for heavy metals sequestration from aquatic environments using various adsorbents, including difficulty in selecting suitable desorption eluent to recover adsorbed heavy metals and regeneration techniques to recycle the spent adsorbents for further use and safe disposal. Therefore, the recovery of adsorbed heavy metal ions and the ability to reuse the spent adsorbents is one of the economic and environmental sustainability approaches. This study presents a state-of-the-art critical review of different desorption agents that could be used to retrieve heavy metals and regenerate the spent adsorbents for further adsorption-desorption processes. Additionally, an attempt was made to discuss and summarize some of the independent factors influencing heavy metals desorption, recovery, and adsorbent regeneration. Furthermore, isotherm and kinetic modeling have been summarized to provide insights into the adsorption-desorption mechanisms of heavy metals. Finally, the review provided future perspectives to provide room for researchers and industry players who are interested in heavy metals desorption, recovery, and spent adsorbents recycling to reduce the high cost of adsorbents reproduction, minimize secondary waste generation, and thereby provide substantial economic and environmental benefits.

A new tannin-based adsorbent synthesized for rapid and selective recovery of palladium and gold: Optimization using central composite design

A tannin-based adsorbent was synthesized by pomegranate peel tannin powder modified with ethylenediamine (PT-ED) for the rapid and selective recovery of palladium and gold. To characterize PT-ED, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS-Mapping), and Fourier transform infrared spectroscopy (FT-IR) were used. Central composite design (CCD) was used for optimization. The kinetic, isotherm, interference of coexisting metal ions, and thermodynamics were studied. The optimal conditions, including Au (III) concentration = 30 m g L - 1 , Pd (II) concentration = 30 m g L - 1 , adsorbent mass = 26 mg, pH = 2, and time = 26 min with the sorption percent more than 99 %, were anticipated for both metals using CCD. Freundlich model and pseudo-second-order expressed the isotherm and kinetic adsorption of the both metals. The inhomogeneity of the adsorbent surface and the multi-layer adsorption of gold and palladium ions on the PT-ED surface are depicted by the Freundlich model. The thermodynamic investigation showed that P d 2 + and A u 3 + ions adsorption via PT-ED was an endothermic, spontaneous, and feasible process. The maximum adsorption capacity of P d 2 + and A u 3 + ions on PT-ED was 261.189 m g g - 1 and 220.277 m g g - 1 , respectively. The probable adsorption mechanism of P d 2 + and A u 3 + ions can be ion exchange and chelation. PT-ED (26 mg) recovered gold and palladium rapidly from the co-existing metals in the printed circuit board (PCB) scrap, including Ca, Zn, Si, Cr, Pb, Ni, Cu, Ba, W, Co, Mn, and Mg with supreme selectivity toward gold and palladium. The results of this work suggest the use of PT-ED with high selectivity and efficiency to recover palladium and gold from secondary sources such as PCB scrap.

Synergistic effect of arsenic removal from petroleum condensate via liquid-liquid extraction: Thermodynamics, kinetics, DFT and McCabe-Thiele method

This work presents the purification of petroleum condensate by removing arsenic ions via liquid-liquid extraction (LLE). Influence of pure and synergistic extractants is investigated. In terms of the practicability, following parameters are examined: the type of extractant, operating time, and temperature. Response surface methodology is used to design parameters such as organic-aqueous ratio and extractant concentration. Under optimal conditions; a mixture of 1 mol/L HCl and 0.02 mol/L thiourea with an organic/aqueous ratio of 1:4 at 323.15 K for 60 min, the extraction of arsenic reached 78.2 %. Further, batch simulation via two-stage counter-current extraction, and estimation by McCabe-Thiele diagram proved to be enhanced arsenic extraction to 95.3 %. Analysis by FTIR show that arsenic ions in petroleum condensate are formed as triphenylarsine compound ((C6H5)3As). The process of arsenic removal proved to be zero-order endothermic, irreversible and spontaneous reaction. The results obtained from the density functional theory (DFT) confirm that arsenic ions react with the synergistic extractant: effectively forming a covalent bond (As-S).

Gold Leaching from an Oxide Ore Using Thiocyanate as a Lixiviant: Process Optimization and Kinetics

Thiocyanate (SCN^-) is a promising alternative to cyanide as a lixiviant for gold extraction and is 1000 times less toxic than cyanide. In this study, the following leaching parameters were tested to optimize the gold recovery for the first time from an oxide ore using the response surface methodology: initial thiocyanate concentration (10-500 mM), initial Fe³⁺ concentration (10-500 mM), and pulp density (10-50% w/v). The maximum gold recovery (96%) was achieved with 500 mM thiocyanate, 100 mM Fe³⁺, and 50% pulp density at 25 °C and pH = 2 for 24 h. A kinetic study on the optimum leaching condition showed that it followed the shrinking core model, in which the rate-controlling mechanism was the diffusion process. These results are discussed in the context of the published literature.