GOLD RECOVERY USING CITRUS SINENSIS PEELS AS BIOADSORBENT

The rapid growth of the electronics industries intensifies the demand for precious rare-earth metals in manufacturing. Gold is one of the extensively consumed metals used in modern chipsets. Hence, the growing demand for gold necessitates the development of sustainable technology to recycle and recover gold from electronic waste (e-waste). Herein, a highly porous, ionic liquid-grafted cationic Zr(IV) metal–organic framework (MOF), named 1′@IL, was strategically synthesized to assess the aqueous-phase extraction of gold. Material 1′@IL exhibited an unprecedented gold adsorption capacity of 1208.5 mg/g within 30 s at neutral pH. Additionally, 1′@IL features extraction of the ultratrace concentration of gold ions from different environmental water matrices (river water, lake water, and seawater) and diverse pH media (pH 2–9). Besides, the long-term physicochemical robustness of 1′@IL assists in the regeneration of the adsorbate and recycling up to six cycles without losing its adsorption capacity, crystallinity, and functionality. The pronounced selectivity and broad operational scope of 1′@IL facilitate effective gold recovery, even from gold-rich electronic waste. In addition, a 1′@IL@PVDF-2 (PVDF = polyvinylidene difluoride) composite membrane was successfully synthesized through the homogeneous distribution of 1′@IL MOF powder over the PVDF matrix. The prepared 1′@IL@PVDF-2 composite membrane demonstrated successful recovery of gold from the aqueous phase with a significantly high adsorption capacity of 850.9 mg/g. Furthermore, electrostatic interaction-based adsorption of gold was precisely elucidated through experimental and theoretical studies. This study provides a clear insight into the potential applications of MOF-based adsorbents for the efficient and targeted extraction of valuable rare-earth elements.

Developing efficient adsorbents for precious metals, especially gold recovery, necessitates the integration of multiple critical properties, including high adsorption capacity, rapid adsorption kinetics, and exceptional selectivity, posing significant scientific challenges with substantial economic and environmental implications. Herein, we report a strategy to achieve highly efficient gold adsorption through synergistic effects of nitrogen and oxygen active sites into covalent organic frameworks (COFs). Two β-ketoenamine-linked COFs (NKCOF-77 and -78) with high-density nitrogen/oxygen active sites are rationally designed and synthesized via a Michael addition-elimination reaction approach. Notably, the comprehensive gold recovery performance for NKCOF-77 is among the best in the COF field, with the third highest adsorption capacity (up to 3225mg g-1), ultrafast adsorption kinetics (<5min), and near-perfect selectivity (>99.9% with 10 competitive cations and anions). Moreover, the COFs show exceptional ability for gold recovery from real e-waste solutions, demonstrating tremendous practical application potential. Various experimental characterization and density functional theory calculations reveal that strategically incorporating high-density nitrogen and oxygen active sites is crucial insignificantly enhancing the gold adsorption capacity. This work provides a novel strategy for designing COFs as precious metal adsorbents, highlighting their promising potential for industrial applications.

Covalent organic frameworks constructed by flexible alkyl amines for efficient gold recovery from leaching solution of e-waste

Reducing preg-robbing in carbonaceous gold ores using passivative or blanking agents

A technology for the recovery of gold from oxidized sulfide gold-copper flotation concentrates using a thiocyanate-based solvent has been developed. The technology involves low-temperature atmospheric oxidation (LTO) of sulfide gold-copper flotation concentrates with sulfuric acid, leaching of gold with a thiocyanate-based solvent, and adsorption of gold on activated carbon or ion-exchange resin. It was found that the recovery of gold into the leaching solution did not exceed 80% when using thiocyanate as a solvent. The recovery of gold from the LTO product of sulfide gold-copper flotation concentrates into the solution by the use of a mixture of thiocyanate and alkali metal cyanide was above 93%, which is comparable to conventional cyanidation. The technology includes preliminary leaching of the oxidized LTO product of flotation concentrates with a thiocyanate-cyanide mixture, at the pulp temperature of 95 oC and the designed concentrations of KSCN and NaCN of 1.0 and 0.5 g/L, correspondingly. Then, the pulp is transferred to adsorption leaching with the countercurrent flow of adsorbent and pulp streams. The main differences between the technology and conventional cyanidation are the elimination of alkaline treatment of the flotation concentrate LTO product; dissolution and adsorption of gold in acidic environments and at a high temperature; the maximum gold leaching time of 7 hours in total compared to 24 hours; the gold solvent (KSCN+NaCN) consumption of 4.5 kg/t of gold concentrate compared to 10 kg (NaCN). An engineering and economical comparison of cyanide and thiocyanate-cyanide for the recovery of gold from oxidized sulfide gold-copper flotation concentrates shows that the technology reduces the capital and operating costs for processing of the LTO product of sulfide gold-copper flotation concentrates by at least 20%.

Natural plant parts such as seeds of Azadirachta indica (neem seeds) and peels of Citrus sinensis (sweet orange) have been used as house-hold remedies against various ailments and bio-pesticides for agricultural purpose due to their repellent, growth regulatory and anti-feedant properties against insects. Despite their beneficial role, these natural insecticides could also have toxic effects on some vital organs of human. Therefore, this study aimed to investigate the sub-acute toxicity of smoke of the Seeds of Azadirachta indica and Peels of Citrus sinensis on the liver, kidney, lungs and heart of swiss albino rats. In this study, three groups of white swiss albino rats were exposed to the smoke of A indica seeds, peels of C sinensis and their combination at different duration of one hour and two hours respectively. The Control group were not exposed to any of the natural insecticides and were fed normal diet and water. After four weeks of the treatment, the animals were all sacrificed and their liver, kidneys, lung and heart were evaluated using standard biochemical and histopathological techniques. The levels of serum biochemical indices for liver (aspartate amino transferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), total bilirubin and protein), kidneys (urea, creatinine and electrolytes), and heart (creatine kinase and lactate dehydrogenase) were found to be significantly higher at (p&amp;lt;0.05) for all the groups treated with the two natural insecticides when compared to control group. Histopathological changes including fibrosis, hemorrhages, vascular congestion and necrosis were observed in the liver, kidneys and lungs tissues of the rats exposed to the smoke of the seeds of A indica. However, no histopathological changes were observed in all organs of rats exposed to the smoke of the peels of C sinensis compared to control group. Moreover, the severity of the effects of smoke of these natural insecticides on both biochemical and histopathological indices increases with increase in duration of exposure. The results of this study revealed that seeds of A indica have significant toxic effects on both the tissue and biochemical markers of all the major organs of the Swiss albino rats, while peels of C sinensis shows effect on only the biochemical indices at the specific duration of time studied.

The exploitation of gold mines of North Greece, which starts soon, and the continually increasing environmental concerns (leading to lower cyanide maximal permitted values in water), make the relative research of considerable interest. With respect to this, a refinement of the gold and silver recovery methods may contribute to cost minimisation of cyanide wastewater treatment. Several researchers have investigated the kinetics of the adsorption of gold and silver by activated carbon from cyanide, thiourea and chloride solutions. Very few works have been reported on gold adsorption by activated carbon from iodineliodide solutions which can be obtained as a downstream leach liquor in wastewater treatment. This work investigates the kinetics of adsorption of gold from iodine solution by activated carbon. It is proved that this kind of adsorption obeys the following kinetic equation: Cb=Co-(Co-Chf)[l-exp(-kt)], where Cb, Cint CO are the concentrations of gold species in the bulk solution at time t, 0, a, respectively. The values of the parameters CO, Cmf, k of this equation are estimated by means of non-linear least squares regression. The k-values estimated in different temperatures give (by similar non-linear regression) a region of activation energy values which indicate, at 95% confidence level, that the critical stage of the process is the diffusion of the gold species in the pores of the activated carbon.

Facile recovery of gold from e-waste by integrating chlorate leaching and selective adsorption using chitosan-based bioadsorbent

Surface functionalized biomass for adsorption and recovery of gold from electronic scrap and refinery wastewater

A review on experimental chemically modified activated carbon to enhance dye and heavy metals adsorption

Gold recovery from electronic waste (e-waste) presents a significant materials challenge, as conventional systems lack structural tunability, exhibit poor metal selectivity, and fail to integrate adsorption and photoreduction functionalities effectively. Herein, we present a topology-guided strategy based on two isomeric π-conjugated covalent organic frameworks (COFs) (v-2D-COF-Dz and v-2D-COF-Pz), incorporating diazine (ortho-N) and pyrazine (para-N) units, respectively, for integrated gold adsorption and photoreduction. The nitrogen topology not only stabilizes the π-conjugated backbone but also significantly modulates the frameworks' optoelectronic and redox properties. Notably, v-2D-COF-Dz exhibits a markedly higher Au3⁺ adsorption capacity (2465versus 1854mgg-1), attributed to enhanced interfacial electron localization and directional charge transfer to Au3⁺ centers. Both frameworks achieve over 99% gold extraction from real e-waste leachates under visible-light irradiation. Spectroscopic characterization and DFT analysis reveal that nitrogen topology governs metal coordination strength and electronic coupling, enabling precise Au-Cl bond activation. This work establishes a nitrogen-topology-directed design paradigm for light-driven, COF-based precious metal recovery systems.

The development of high-performance adsorbents with exceptional adsorption capacity, superior selectivity, and excellent regenerability is crucial for sustainable precious metal recovery. Functionalized metal–organic frameworks (MOFs) show particular promise in this regard, where the strategic incorporation of functional groups can significantly enhance adsorption performance. In this study, we developed a series of MIL-101(Fe) with tunable compositions by varying the ratio of the two organic ligands. The amino-functionalized NH2-MIL-101(Fe) demonstrated outstanding gold (Au(III)) recovery performance from electronic waste wastewater, achieving an experimentally measured adsorption capacity of 4077.47 mg·g–1 at 308 K while maintaining excellent regenerability over multiple cycles without significant capacity loss. Comprehensive investigation of adsorption kinetics and thermodynamics, along with systematic evaluation of pH effects and competitive ions, revealed the material’s robust performance under various conditions. Remarkably, NH2-MIL-101(Fe) exhibited exceptional selectivity for Au(III) recovery, even in complex real leaching solutions from central processing units (CPUs) and random access memory (RAM) containing high concentrations of interfering ions. To facilitate practical application, we successfully immobilized NH2-MIL-101(Fe) on expanded perlite, creating a composite material that maintained a high gold recovery efficiency during prolonged operation in simulated wastewater. Mechanistic studies demonstrated that the exceptional performance stemmed from synergistic effects between amino group coordination and Fe-node-mediated reduction, where introduced –NH2 groups played a pivotal role in both Au(III) adsorption and reduction to Au(0). This work not only presents a highly efficient and selective adsorbent for gold recovery but also provides valuable insights into designing functionalized MOF materials for sustainable resource recovery from electronic waste.

Citrus sinensis peel polyphenols loaded alginate nanoparticles: Enhanced stability and anti-diabetic efficacy via bidirectional AMPK regulation and NF-кB suppression.

Water pollution caused by various natural and artificial sources such as expansion of industrialization, rapid increment in population size, the threat of climate change, and development in urbanization takes a serious attention. Due to this fact, various protocols and techniques were adopted for the treatment of such polluted water. In the present findings, TiO2 nanoparticles (NPs) and TiO2/rGO nanocomposites (NCs) were synthesized using titanium tetra butoxide in the presence of Citrus sinensis (CS) and Musa acuminata (MA) peel waste extract as a capping, reducing, and stabilizing agent. The synthesized NPs and NCs were characterized using thermogravimetric-differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) pattern, ultraviolet diffuse reflectance spectroscopy (UV-DRS), and Fourier transform infrared (FTIR) spectroscopy. The synthesized NPs and NCs were investigated as green alternative photocatalyst for the degradation of methylene blue (MB) dye under visible light irradiation. Thermal analysis results confirmed that the green synthesized TiO2 NPs were found to be too stable above 550°C. XRD analysis result showed that the average crystalline size of CS and MA mediated synthesized TiO2 NPs with various volume ratios was in the range of 7.3–27.3 nm and 13.4–22.4 nm, respectively. The average crystalline size of CS and MA peel extract template synthesized TiO2/rGO NCs was found to be in the range of 7.5–15.3 and 11.2–12.5 nm, respectively. The band gap energy was calculated to be in the range of 3.17–3.29 eV and 3.10–3.38 eV for the CS and MA mediated synthesized TiO2 NPs, respectively. Eg of CS and MA peel extract template formed TiO2/rGO NCs was found to be in the range of 2.85–3.11 eV and 3.07–3.11 eV, respectively. SEM analysis proved that the various synthesized TiO2 NPs and TiO2/rGO NCs were spherical in shape and the absence of any other foreign materials confirmed the purity of the corresponding nanocatalysts. In addition, TEM, HRTEM, and SAED analysis confirmed that the structures of the synthesized nanocatalysts were spherical in shape and the catalysts were too crystalline and the result was found to fit with the XRD result. Among the synthesized various volume ratios of TiO2 nanocatalysts, high percentage of degradation (62% and 58.2%) was achieved using TiO2-2c and TiO2-2 m, respectively. Moreover, 94.28% and 94.25% of MB degradation were achieved in the presence of TiO2/rGO-1.5c and TiO2/rGO-1.5c nanocomposite photocatalysts, respectively.

Granular polyacrylonitrile with internal 3D channels for gold recovery from thiosulfate solution