Activated Hard Shell of Apricot Stones： A Promising Adsorbent in Gold Recovery

Activated carbon has been proven to be an effective adsorbent for the recovery of a wide variety of metal ions from aqueous solutions. In this research, the activated hard shell of Iranian apricot stones was used for gold recovery from electro-plating wastewater. The effect of parameters such as dose and particle size of adsorbent,pH, agitation speed of mixing on the gold recovery was investigated. The results showed that under the optimum operating conditions more than 98% of gold ions were adsorbed onto activated carbon after just 3 h. In addition, the adsorbed gold could be eluted from this adsorbent by improved striping method. The process involves contact of gold-laden adsorbent with a strong base at ambient temperatures followed by elution with an aqueous solution containing an organic solvent. It was found that activated hard shell of apricot stones has the potential to replace im ported commercial activated carbons in gold adsorption processes.

Kinetic studies of gold recovery from dilute aqueous solutions using Fe^(2+) chloride ions

The kinetics of Au3＋ chloride complex ions reduction using Fe2＋ chloride ions was investigated by stopped-flow method. The influence of initial concentrations of Au3＋ chloride ions, Fe2＋ ions, chloride ions, neutral salt （NaC104）, pH of the solution and temperature was investigated. Activation energy was determined to be 42.36 kJ/mol. Moreover, the kinetic equation was postulated. Obtained solid phase was analyzed using SEM techniques. Particles size varies in the range from 0.5 to 5 gm. It was shown that gold can be removed from the solution by the reduction ofAu3＋ chloride ions and filtration of precipitant.

Influence of Copper and Arsenic on Gold Recovery in the Yalea Deposit, Western Mali

Gold recovery process is well known. The following paper presents the problematic related to the influence of Copper and Arsenic on the recovery of gold in the Yalea deposit. Multielement tests (Au, Cu, As) carried out on 37 blocks made it possible to understand that there is a correlation between these elements. This correlation has been observed since the analysis of block models (the block model for Copper, block model for Arsenic and the block model for gold. These models have shown that the Yalea deposit areas with a high gold content correspond to areas of high copper content and arsenic. Those who made it clear that copper and Arsenic are tracing elements of Gold in the Yalea deposit. In this paper, the mineralurgical tests carried out on 28 blocks revealed that the copper and the arsenic content in the ore penalize the recovery of Gold (146 ppm for copper and 4710 ppm for Arsenic). The Yalea deposit was emplaced by several hydrothermal phases that reactivated the structures. These phases are responsible for the establishment of large quantities of copper sulphides. Copper and Arsenic are elements that have a considerable influence on the gold recovery in the Yalea deposit.

Polyaniline-poly(vinylidene fluoride) blend microfiltration membrane and its spontaneous gold recovery application

Structural regular polyaniline was synthesized via a modified-chemical oxidative polymerization reaction. Highly hydrophilic polyaniline(PANi) and polyaniline-poly(vinylidene fluoride) blend(PANi-PVDF) membranes were prepared by solution casting and phase inversion techniques. Both of the mechanical and filtration properties of the membranes depend on the polymer composition and doping level of the blends. The elasticity of the membrane is greatly improved upon introducing poly(vinylidene fluoride) into the blend. The water permeability of the blend membranes is further enhanced when the membranes are doped with hydrochloric acid. The PANi-PVDF blend membranes are capable of recovering metallic gold from the acid/halide leaching streams spontaneous and sustainably, and are promising candidates for wastewater treatments in electronic industries.

Functional Polyselenoureas for Selective Gold Recovery Prepared from Catalyst-Free Multicomponent Polymerizations of Elemental Selenium

Selenium-containing polymers with fascinating functionalities such as stimuli-responsive property,enzyme mimics,antioxidant activity,promotion of immune-cell activity,anticancer activity,and controlled delivery property,are highly desired,but rarely developed due to their underexplored synthetic methods.Herein,through careful design of monomeric structures and polymerization conditions,we report a series of catalyst-free multicomponent polymerizations(MCPs)of elemental selenium with aliphatic/aromatic diamines and diisocyanides that directly converted selenium to polyselenoureas with long-term stability,good solubility,well-characterized structures,and unique functionalities.The MCPs enjoyed broad monomer scope and fast conversion in 1 min,delivering 18 polyselenoureas with high molecular weights(M_(w)s up to 94,600 g/mol)in high yields(up to 99%).Furthermore,the polyselenoureas could be used for the extraction of Au^(3+)from mixed-metal ion solutions under practical conditions with high selectivity,sensitivity(<1μg/L),efficiency(>99.99%),and capacity(up to 665.60 mg·Au^(3+)/g)within 1 min.Further,the elemental gold was recoverable after the pyrolysis of the polymer complexes.

Improving gold recovery of Pb–Zn sulfide ore by selective activation with organic acid

Free gold and gold wrapped in sulfides are considered as the object of gold floatation. However,floatation of free gold exhibits more variables in practice.In this study, improving gold recovery of a Pb-Zn sulfide ore from Yunnan Province, China, was investigated. The results show that free gold and auriferous sulfides account for 94.99 % of total gold. Without adding organic acid in floatation, only 82 % recovery of gold could be obtained.Gold recovery in Au/Pb concentrates increases by 9.29 %with oxalate added and by 7.35 % with citric acid added,respectively, while performances of lead and arsenic nearly keep a constant. A possible reason is that free gold is of wonderful selectivity against pyrite with organic activators.A new method to enhance gold recovery is proposed.

Removal, Recovery and Recycle of Gold (III) from Aqueous Solution Using Persimmon Tannin Gel

In order to recover much amount of gold, gold removal-recovery cycle was examined using immobilized persimmon gel, which could remove much amount of gold (III) from the tetrachloroaurate solution at 30°C. Removal of gold has proceeded different 2 mechanisms stages. At first, gold (III) was adsorbed rapidly on the surface of the persimmon gels until 2 hours and reached adsorption equilibrium. After that, the amount of gold removed was re-increased slowly and also reached equilibrium until 48 hours. The amount of gold removed was affected by the pH of the solution. The amount of Au removed was the highest at pH 5, which was decreased with decreasing or increasing the pH of the solution. The amount of gold removed (mol/g-dry wt. gels) was increased with increasing the gold concentration in the solution, whereas gold removed ratio was decreased. Gold removed ratio was increased with increasing the amount of persimmon gel used, whereas the amount of removed Au (mol/g-dry wt. gels) was decreased. Gold removal-recovery cycles were also examined in detail.

A core–shell amidoxime electrospun nanofiber affinity membrane for rapid recovery Au(Ⅲ) from water

An affinity membrane was prepared by coaxial electrospinning and amidoxime(AONFA),and it was applied to selectively recovery Au(Ⅲ)from an aqueous solution.The static adsorption results showed that,when p H at 5,the maximum adsorption capacity of AONFA membrane for Au(Ⅲ)was 509.3 mg·g^(-1).AONFA membrane exhibit much higher affinity and selectivity towards Au(Ⅲ)than other metal cations.The membrane could be regenerated effectively by mixture solution of thiourea and HCl,and the desorption ratio reached almost 100%after 4 hours desorption.The dead-end filtration results showed that,the membrane utilization efficiency and adsorption capacity can be improved by increasing the flow rate,while increasing the concentration shorted the breakthrough process and had little impact to adsorption capacity.We can flexibly adjust the flow rate and concentration according to the situation to obtain the maximum utilization efficiency of the membrane in filtration process.The dynamic adsorption capacity is higher than the static adsorption capacity.The adsorption mechanism for Au(Ⅲ)is electrostatic adsorption and reduction.Thus,AONFA membrane filtration was demonstrated to be a promising method for continuous recover Au(Ⅲ)from wastewater.

A MOF/poly(thioctic acid)composite for enhanced gold extraction from water matrices

With the fast generation of electronic waste(e-waste)and the increasing depletion of metal resources,“urban mining”that can selectively recover gold from secondary resources has attracted great interest.Construction of materials with high extraction capacity and satisfying selectivity in complex aqueous-based matrices still remains challenging.Here,a novel metal-organic framework/polymer composite(Fe-BTC/poly(thioctic acid),denoted as Fe-BTC/pTA)has been newly synthesized and applied for selective gold recovery in different matrices(river water,seawater,and leaching solution of e-waste).Benefiting from the high specific surface area and suitable pore sizes as well as the rational design of active sites,the composite exhibits high adsorption capacity(920 mg/g),high removal efficiency(>99%),fast kinetics(below 0.1 ppb within 10 min),and good applicability in complex matrices,which are better than those of most reported sulfur-containing adsorbents.Solid-state metallic gold with high purity can be effectively enriched due to the high recyclability and long-term stability of the composite.The material after adsorption can be further applied as a heterogeneous catalyst for water remediation due to the in situ generated gold nanoparticles by the redox reaction between Au(III)ions and the S-containing groups in the composites.

A portable and washable solar steam evaporator based on graphene and recycled gold for efficient point-of-use water purification

A solar steam evaporator provides a sustainable and efficient alternative water purification solution to address the global freshwater shortage.Previous efforts have made significant advances in maximizing its water evaporation rate,but no single evaporator has all the properties necessary for practical point-of-use application,including a high efficiency for generation of drinkable water,an excellent portability critical for on-site water purification,good washability for mitigating evaporator fouling,and good reusability.We report a strategy to produce a high-performance photothermal material for point-of-use water purification.By simultaneously incorporating graphene and gold particles grown from recycled electronic waste in a mechanically strong sponge,we achieved highly efficient water purification under realistic conditions.In addition to a high evaporation rate(3.55 kg/m^(2)/h under one-sun irradiation)attributed to a control of atomic structure of graphene and the size-dependent surface plasmon resonance of gold nanoparticles,it is portable which can be folded,vacuum compacted,dried and rehydrated without compromising performance.It also allows repeated washing to remove contaminant fouling so that it can be reused.The evaporator transforms various types of contaminated water into drinkable clean water,and can be mounted at any angle to optimize the incident solar irradiation.Furthermore,the assembled steam evaporator device could gain purified water meeting the World Health Organization drinking water standards with a high evaporation rate of 9.36 kg/m^(2)/h under outdoor sunlight.