Electrochemical behaviors of gold and its associated elements in various complex agent solutions

1　INTRODUCTIONGoldisquitestableanddifficulttodissolveinacommonmineralacid .However ,becausethereisadelectroniclayerunfilledingoldatomicstructure ,goldcanbecombinedwithmanychemicalagentstoformstablecomplexions,causingthepotentialofgoldinasolutiontodecreaseandgoldtodissolveinthesolutioneasily .Basedonthisprinciple ,cyanideisanefficientlixiviatingagentofgold ,andhasbeenwidelyusedtoextractgoldfrom primaryandsecondaryresources .However ,itisthemosttoxicandnotbeneficialtoen vironmentprotection…     

Study on mechanism of gold leaching by thiourea in the presence of sodium sulphite

Ｃｙａｎｉｄａｔｉｏｎｈａｓｂｅｅｎｕｓｅｄｆｏｒｍｏｒｅｔｈａｎｏｎｅｈｕｎ ｄｒｅｄｙｅａｒｓｉｎｇｏｌｄｉｎｄｕｓｔｒｙｓｉｎｃｅｔｈｅｆｉｒｓｔｐａｔｅｎｔｂｙＭａｃＡｒｔｈｕｒａｎｄｔｈｅＦｏｒｒｅｓｔｓｉｎ 1889[1] ,ａｎｄｓｔｉｌｌｒｅｍａｉｎｓｔｈｅｍｏｓｔｐｏｐｕｌａｒｏｐｔｉｏｎｆｏｒｐｒｏｃｅｓｓｉｎｇｇｏｌｄｏｒｅｓｂｅｃａｕｓｅｏｆｉｔｓｐｒｏｃｅｓｓｓｉｍｐｌｉｃｉｔｙａｎｄｏｐｅｒａｔｉｏｎｅｃｏｎｏｍｙ .Ｎｅｖｅｒｔｈｅ ｌｅｓｓ,ａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅｔｅ…     

HYDROPHOBICITY－HYDROPHILICITY BALANCE RELATIONSHIPSFORCOLLECTORLESSFLOTATIONOFSULPHIDEMINERALS

ＨＹＤＲＯＰＨＯＢＩＣＩＴＹ－ＨＹＤＲＯＰＨＩＬＩＣＩＴＹＢＡＬＡＮＣＥＲＥＬＡＴＩＯＮＳＨＩＰＳＦＯＲＣＯＬＬＥＣＴＯＲＬＥＳＳＦＬＯＴＡＴＩＯＮＯＦＳＵＬＰＨＩＤＥＭＩＮＥＲＡＬＳＨＹＤＲＯＰＨＯＢＩＣＩＴＹ－ＨＹＤＲＯＰＨＩＬＩＣＩＴＹＢＡＬＡ...     

Optimization of efficient stable reagent of alkaline thiourea solution for gold leaching

1　INTRODUCTIONThiourea ,asanontoxic goldleachingreagentsubstitutingcyanide ,hasattractedtheinterestofmanyresearchersallovertheworldsincethedissolu tionofgoldinthioureasolutionwasfirstreportedin194 1,andaseriesofstudiesonthetheoryandtech nologyforleachinggoldbythioureahavebeencon ducted[1 3] .Mostreportson golddissolutioninthioureasolutionwereconcernedwithacidicmedia .Itwasdifficultforgoldtodissolveinalkalinesolutionbecauseofthepassivationofelementsulfurproducedbytheirreversibledecompositi…     

Direct rapid determination of traces of sulfide in environment samples

An improved ethylene blue method for determination of sulfide is developed. It has been adapted to a direct determination of sulfide by both common spectrophotometric method and total differential spectrophotometric method. In common spectrophotometric method, the calibration curve is A=1.69ρ+0.006 and the correlation coefficient is 0.9994.The apparent molar absorptivity is 5.42×104 L*mol-1*cm-1 and calibration curve is liner when ρ is in the range of 0-0.9 mg*L-1. In total differential spectrophotometric method, the calibration curve is A=9.25ρ+0.004 and the correlation coefficient is 0.9996. The apparent molar absorptivity is 2.96×105 L*mol-1*cm-1and calibration curve is liner when ρ is in the range of 0-0.10 mg*L-1. The sensitivity of this method is increased significantly compared with the former ethylene blue method. The speed of reaction is also faster than the former one. The limit of detection is found to be 1.0 ng*mL-1 by both common spectrophotometric method and total differential spectrophotometric method. Ten replicate analyses of a sample solution containing 100 ng*mL-1sulfide give a relative standard deviation of 1.8%. The effects of various cations and anions on the determination of sulfide are studied and procedures for removal of interference is described. The method is used for the determination of sulfide in environment samples with satisfactory results.     

Enhancement of natural ventilation in rectangular enclosure with two openings by thin fin

A numerical method was used to study the natural ventilation in a rectangular enclosure with two symmetrical openings. In order to improve the natural ventilation efficiency, a fin was introduced into the enclosure. Steady-state heat transfer by laminar natural ventilation in a partially divided rectangular enclosure was investigated by numerically solving equations of mass, momentum and energy. Streamlines and isotherms were produced and heat transfer rate were calculated. A parametric study was carried out using the following parameters: Rayleigh number (1×10³ − 1×10⁶), dimensionless length (0–0.7) and position values (−0.7−0.7). It is found that the Nusselt number is an increasing function of Rayleigh number. By comparing with no-fin case, it is concluded that fin can effectively enhance the natural ventilation in the enclosure. Foundation item: Project(50408019) supported by the National Natural Science Foundation of China     

Mechanism of zinc electroplating in alkaline zincate solution

The cathodic deposition properties and mechanism of Zn in alkaline zincate solution were studied by electrochemical techniques. The results show that Zn2 exists in the alkaline solution in the form of Zn(OH)42-. The apparent activation energy of the electrode reaction is 38.93 kJ/mol, which indicates that the discharge of Zn(OH)42- on cathode is controlled by electrochemical polarization, and accompanied by a preceding chemical reaction. The diffusion coefficient of Zn(OH)42- is 2.452×10-6 cm2/s. Zn(OH)2 is the species directly discharged on the cathode surface. Based on the above results the mechanism of zinc electroplating in alkaline zincate solution was put forward. The discharged species is Zn(OH)2 formed from the preceding chemical reaction, which becomes Zn(OH)ad when gaining one electron, and then gaining the second electron to become Zn. The first electron gaining step is rate determining one.     

Physical simulation of hot deformation of TiAI based alloy

In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti-49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1 100 ℃ with strain rates of 10^-3-10^-1 s^-1. Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n, has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ = K1 drex^-0.56. The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lgdrex= -0.281 1gZ 3.908 1.     

SELECTIVE DISSOLUTION OF GOLD IN AN ALKALINETHIOUREA SOLUTION BY ELECTROLYSIS

Thioureawaswellknownasanlixiviantforgoldearlyin1932[fi.Thedissolutionofgoldinacidicthioureasolutionwasreportedin1941byPlaksin[Zj.Thioureahasbeenwidelypaidattentiontoasahighselectivenontoxicnovellixiviantofgoldsince197013j.Electrochemicalexperimentsongoldelectrodeshavebeenconductedbymanyresearches,showingthatgolddissolutionbythioureaismoreefficientinacidicsolutionthaninneutralandalkalinesolutions[4j.Theprocessforextract'inggoldfromtheoreorscrapbyacidicthioureasolution,however,demandedexcessive…     

Dynamics of electrodeposition of tetraethylthioram disulphide (TETD) on pyrite surface

Ｄｉｅｔｈｙｌｄｉｔｈｉｏｃａｒｂａｍａｔｅ(ＤＤＴＣ)ｉｓｏｎｅｏｆｔｈｅｍｏｓｔｆｒｅｑｕｅｎｔｌｙｕｓｅｄｃｏｌｌｅｃｔｏｒｆｏｒｆｌｏｔａｔｉｏｎｏｆｈｅａｖｙ ｍｅｔａｌｓｕｌｆｉｄｅｍｉｎｅｒａｌｓ,ｓｕｃｈａｓｇａｌｅｎａ ,ｃｈａｌｃｏｐｙｒｉｔｅａｎｄｊａｍｅｓｏｎｉｔｅ ,ａｎｄｓｈｏｗｓｓｔｒｏｎｇｓｅ ｌｅｃｔｉｖｉｔｙ[1] .ＩｔｉｓｒｅｐｏｒｔｅｄｔｈａｔＤＤＴＣｉｓａｐｏｗｅｒｆｕｌｃｏｌｌｅｃｔｏｒｆｏｒｇａｌｅｎａａｎｄｖｅｒｙｓｅｌｅｃｔｉｖｅａｇａｉｎｓｔｐｙｒｉｔｅｉ…     

Enhancement of flow boiling heat transfer with surfactant

The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1 × 10⁻⁵ −5 × 10⁻⁵. In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions. Foundation item: The Natural Science Foundation of Tianjin(No. 94220) Biography of the first author: QIU Yun-ren, doctoral student, born in Dec. 1966, majoring in heat and mass transfer in chemical engineering.     

Investigation on the surface active sites variation of mineral dusts

Ｔｈｅｇｒｏｕｐｏｆｎａｔｕｒａｌｍｉｎｅｒａｌｄｕｓｔｓｒｅｌａｔｅｓｔｏｔｈｅｉｒｂｉｏｌｏｇｉｃａｌａｃｔｉｖｉｔｙａｎｄｃｏｎｔｒｏｌｓｔｈｅｉｒｆｅａｔｕｒｅａｎｄｃｏｎｔｒｉｂｕｔｉｏｎｏｆｓｕｒｆａｃｅａｃｔｉｖｅｓｉｔｅｓａｎｄｉｎｆｌｕ ｅｎｃｅｓｏｎｔｈｅｐｒｏｃｅｓｓｏｆｔｈｅｉｒｓｕｒｆａｃｅ/ｃｅｌｌｐｈｙｃｏ ｃｈｅｍｉｓｔｒｙ[1] .1　ＥｘｐｅｒｉｍｅｎｔａｌＴｈｅｓａｍｐｌｅｓｕｓｅｄｉｎｅｘｐｅｒｉｍｅｎｔａｌｗｅｒｅｆｉ ｂｒｏｕｓｂｒｕｃｉｔｅｆｒｏｍｔｈｅｓｏｕ…     

Isotope systematics and metallogenetic age of Zhuanghe gold deposit, Liaoning province, China

Based on the metallogenetic geology conditions, the H, O, C and S isotopic compositions were measured by MAT-251 mass spectrometer, and Pb isotope and Rb-Sr dating were carried with MAT-261 multi-acceptor mass spectrometer. The results show that the δ18O values of gold-bearing vein quartz from different levels are 1.19%-1.42%. The calculated δ18O values of ore fluids are 0.55%-0.78%, and δD values are from –8.64% to –6.66%. The calculated values of δ 34 SH2Sby the δ34Spy values in quartz veins display sulfur isotope compositions from -0.053% to 0.413%. Carbon isotope compositions of carbonates are from -0.612% to 0.140%. The mole ratios of 206Pb to 204Pb, 207Pb to 204Pb and 208Pb to 204Pb in auriferous quartz vein are 16.987-17.545, 15.342-15.623, and 38.254-38.744, respectively. The age of the Zhuanghe gold deposit determined by Rb-Sr isochron of the fluid inclusions in quartzes is (143.0±5.8) Ma. These isotopic data suggest that the metallogenetic fluids are generated from magmatic hydrotherm and the origin of ore-forming matters is related to the deep-derived magmatic activities. Meanwhile, the metallogenetic epoch of the Zhuanghe gold deposit is in Yanshanian period.     

Surface modification of magnesium hydroxide by γ-aminopropyltriethoxysilane

Magnesium hydroxide（MH）,which is commonly used as a halogen-free flame retardant filler in composite materials,was modified by silanization reaction with γ-aminopropyltriethoxysilane （γ-APS） in aqueous solution at different pH values （pH range from 8.0 to 12.0）. The surface properties of grafted γ-APS on MH surface as a function of solution pH value were studied using elemental analysis,Fourier transform infrared spectroscopy and zeta potential measurement. The results show that hydrolysis and condensation of γ-APS are activated in alkaline solution and lead to multilayer adsorption of γ-APS molecules on the surface of MH. The type of adsorption orientation of γ-APS on MH surface is a function of coverage density that is altered by changing solution pH value. At low coverage density （e.g. 55 nm^-2）,γ-APS molecules are preferentially adsorbed to the surface with the silicon moiety towards the surface,and increasing coverage density （e.g. 90 nm^-2） leads to parallel orientation. At an even higher coverage density （e.g. 115 nm^-2）,γ-APS molecules bond to the surface with the amino moiety towards the surface.     

Kinetics of Zn cathodic deposition in alkaline zincate solution

Kinetic parameters of the electrode reactions were measured by investigating steady-state current-potential behaviors. The Tafel slopes of cathodic and anodic processes are -0.113 8 V and -0.041 18 V, the anodic and cathodic apparent transfer coefficients are 0.519 3 and 1.435 2, respectively, and the stoichiometric number of rate-deterrnining step is 1. The theoretical kinetics equation of electrode reaction was deduced, from which the dynamic parameters can be calculated as follows： the cathodic and anodic Tafel slopes are -0.118 V and -0.039 4 V, respectively, consisting with the experimental values, Finally, the correctness of the mechanism was further demonstrated using apparent transfer coefficient according to the electrochemical dynamic equation of multi-electron reaction.     

Quality evaluation of layerlike backfilling and flow pattern of backfill slurry in stope

Stability condition and quality evaluation formula of layerlike backfilling roof,Q≥C,where Q denotes is quality index depending on allowable compressive or tensile strength and integrity of backfilling,and C is the technical index depending on mining method and backfilling technology,were inferred according to simply supported beam theorem.Technical treatment measures for instable backfilling roof,including optimum of appropriate filling materials and dosage for excellent flow property and reduction of backfill cost.It is proved that slope equation of backfill slurry in a stope to be filled is y=hexp[x2/(2σ)2)],where h is height of cone and σ2 is mean square,and that optimum drainage point of backfill slurry can be determined by the equation and sizes of stope.Case study indicates that the results can give a theoretical support for quality evaluation and control of layerlike backfilling.     

Drag reduction of flow boiling with polymer additives

Ｓｏｍｅｓｔｕｄｉｅｓｗｅｒｅｄｏｎｅｏｎｐｏｏｌｂｏｉｌｉｎｇｈｅａｔｔｒａｎｓｆｅｒｏｆａｄｄｉｔｉｖｅａｑｕｅｏｕｓｓｏｌｕｔｉｏｎ ,ｂｕｔｌｉｔｔｌｅｏｎｆｌｏｗｂｏｉｌｉｎｇ[1 3] .Ｔｈｅｕｓｅｄａｄｄｉｔｉｖｅｓａｒｅｓｕｒｆａｃｔａｎｔａｄｄｉｔｉｖｅｓａｎｄｐｏｌｙｍｅｒａｄｄｉｔｉｖｅｓ[1 4] .Ｉｎｖｅｓｔｉｇａｔｉｏｎｓｏｎｔｈｅｄｒａｇｒｅｄｕｃｔｉｏｎｏｆａｄｄｉｔｉｖｅｓａｒｅｕｓｕａｌｌｙｃｏｎ ｃｅｎｔｒａｔｅｄｏｎｓｉｎｇｌｅｐｈａｓｅｆｌｏｗ[5 ] ,ｏｒｒａｔｈｅｒ,…     

Chemial Bond and Stability of Adsorption of [Au（ AsS3 ）]^2- on the Surface of Kaolinite

Density function theory and discrete variation method (DFT-DVM) were used to study the adsorption of [Au( AsS3 )]^2- on the surface of kaolinite. The correlation among structure, chemical bond and stability was discussed. Several models were selected with [ Au( AsS3)]^2- in different directions and sites. The results show that the models with gold on the edge of kaolinite basal layer contain pincerlike bond among gold and several oxygen atoms and form strong Au - 0 covalent bond, so these models are more stable than those with gold above or under the layer. The models with gold near to [ AlO2(OH)4] octahedra are more stable than those with gold near to the vacancy withont aluminium. These two stable tendencies in kaolinite- [ Au( AsS3)]^2- are stronger than that in kaolinite-Au systems. The interaction between [ Au( AsS3 )]^2- and kaolinite is stronger than that between gold and kaolinite, and this interaction is strong enough to form the surface complexes.     

Synthesis of 1,4-benzenedicarbonyl thiourea resins and their adsorption properties for Ag（I）

Several 1,4-benzenedicarbonyl thiourea resins (BTR) were synthesized through interfacial polymerization between 1,4-benzenedicarbonyl diisothiocyanate and polyamine. Their structures were confirmed by FT-IR. The adsorption properties (including the effect of adsorption time, pH, initial concentrations and temperature) of BTR-1, BTR-2 and BTR-3 for Ag(I) were investigated by batch tests. The results show that the adsorption equilibria of BTR-1, BTR-2, BTR-3 for Ag(I) are achieved after about 10 h. Their equilibrium adsorption capacities are 7.11, 6.75 and 6.23, respectively, and the adsorption process accords with G. E. Boyd equation and Langmuir adsorption isotherm as well. The adsorption capacities increase with the increase of pH (the highest uptake values are observed at pH being about 6–7). The thermodynamic parameters of BTR-1 were calculated. The results show that ΔH ^Θ; and ΔS ^Θ are 6 958.8 J/mol and 64.28 J/(mol·K), respectively, and ΔG ^Θ at 20, 30, 40 and 50 °C are −11.79, −12.52, −13.16 and −13.8 kJ/mol, respectively. The silver-loaded resins can be quantitatively eluted by a solution containing 6% thiourea in 1 mol/L HNO₃.     

Separation of xylo-oligosaccharides from enzymatic hydrolytes using membrane reactor

1　INTRODUCTIONMembranereactorsrepresentapromisingtech nologyforproductionandprocessinginthepharma ceuticalandfoodindustry .Theincreasingattentionto“natural like” productsandenviron mentalpro cessesmakesthemembranereactorsparticularlyat tractive,becausetheydonotrequirechemicaladdi tives ,areabletoworkundermildconditionsofpH ,temperature,and pressure ,andcanreducethefor mationofby products[1] .Thecatalyticactionofen zymesisextremelyefficientandselectivecomparedwithordinarychemicalcatalys…