197 Au Mössbauer study of the gold species adsorbed on carbon from cyanide solutions

The gold species present on activated carbon after adsorption from solutions of Au(CN)₂ ^? have been studied by¹⁹⁷Au Mössbauer spectroscopy as a function of the pH value of the solution, the loading of the carbon, the coadsorption of polyvalent cations, and the treatment of the samples after adsorption. The gold was found to be adsorbed mainly as Au(CN)₂ ^?. Coadsorbed polyvalent cations (Ca^²+, Gd^³+) have no influence on the Mössbauer parameters of the adsorbed gold complex. After adsorption from acidic solutions (pH ? 4), one finds a substantial amount of adsorbed gold with Mössbauer parameters similar to those of crystalline AuCN. Presumably, this gold is bound in Au_x(CN)_x+1 oligomers which form during drying. An additional product with Mössbauer parameters close to those of KAu(CN)₂Cl₂ was observed on dried samples after adsorption at pH 1. A minor gold species with an uncommonly small electric quadrupole splitting was found on wet carbons but disappeared on drying.     

Reaction mechanism of gold dissolution with bromine

The dissolution of gold with elemental bromine was studied by using a rotating disc technique. The main parameters studied were bromine and bromide concentrations, stirring speed, pH, and temperature. The effect of various salts, manganese, and hydrogen peroxide was also examined. The dissolution kinetics of gold with Br₂ and NaBr mixture is complex. The reaction mechanism is a function of solution composition, which determines the kind of adsorbing species. For an excess concentration of bromide ions, the rate expression is Rate = (2k _cl7 k _al6)^1/2 K ₁₅ [Br ₃ ⁻ ] and for an excess concentration of bromine, the rate expression is Rate = (2k _c27 k _a29)^1/2 [Br⁻]^1/2 {K₂₅ [Br₂]³/(1 +K ₂₅ [Br₂]³)}^1/2 Gold in bromine solutions dissolves according to electrochemical/chemical (EC) mechanisms. The electrochemical component of the mechanism is responsible for the formation of AuBr₂. In the chemical component of the mechanism, this monovalent gold bromide disproportionates into gold and stable AuBr ₄ ⁻ , which reports into solution. With respect to pH, there are two characteristic dissolution regions. In the pH range of 1 to 7, gold dissolution rates were insensitive to pH. Above pH 7, gold dissolution rates decreased with increase of pH.     

Substitution Recovery of Gold from Copper-Ethylenediamine-Thiosulfate Leaching Solution with Copper Power

The substitution method of recovering gold from thiosulfate-ethylenediamine (en)-Cu²⁺ leaching solution using copper powder was studied. The effects of reaction time, stirring speed, pH, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature on gold recovery were systematically examined. The experimental results showed that reaction time, stirring speed, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature have a significant influence on the recovery rate of gold, whereas the pH has little effect. A high gold recovery rate of 95.38% was achieved in 0.2 mol/L thiosulfate at 40°C after 40 min with a stirring speed of 400 rpm, pH of 11, en/Cu²⁺ molar ratio of 6, and Cu/Au⁺ mass ratio of 150. A kinetic study revealed that the reduction of gold-thiosulfate complex ions (Au(S₂O₃) ₂ ^3- ) on the surface of copper powder follows a first-order kinetics model with an apparent activation energy of 39.82 kJ/mol.     

The reversibility of adsorption of gold cyanide on activated carbon

Much controversy exists about the mechanism by which gold cyanide adsorbs on activated carbon. It is not the purpose of this article to explain the exact adsorption mechanism but, rather, to investigate the factors affecting the reversibility of adsorbed gold cyanide. Whereas Au(CN) ₂ ⁻ is soluble in water, AuCN and Au require the addition of cyanide to form Au(CN) ₂ ⁻ . The reversibility of the adsorption of gold onto carbon is a function of the nature of the adsorbed gold and determines the need for cyanide in the elution process, which affects the operating costs of a carbon-in-pulp (CIP) plant. The fraction of adsorbed Au(CN) ₂ ⁻ that will be decomposed to AuCN was found to be a function of the pH and temperature of the solution and the type of activated carbon used. It was observed that two different batches of carbon from the same manufacturer yielded widely different ratios of AuCN to Au(CN) ₂ ⁻ , although their specifications did not differ much. These results were confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). A combination of low pH and high temperature, as is found in the hot acid wash step of an AARL elution, leads to the reduction of both Au⁽¹⁾ species to metallic gold, Au⁽⁰⁾. The fraction of the adsorbed Au(CN) ₂ ⁻ that is converted to AuCN or Au⁽⁰⁾ no longer participates in the equilibrium between Au(CN) ₂ ⁻ in solution and Au(CN) ₂ ⁻ in the adsorbed phase. It was observed that the isotherm for desorption is higher than the isotherm for adsorption by a percentage which is, on average, equal to the percentage of Au(CN) ₂ ⁻ converted to AuCN or Au⁽⁰⁾.     

The mechanism of elution of gold cyanide from activated carbon

Numerous articles have appeared on the mechanism of the adsorption of gold cyanide onto activated carbon. In contrast, little information is available on the mechanism of elution of the adsorbed gold. It is the objective of this article to formulate such a mechanism on the basis of batch and column elution tests without analyzing adsorbed species on the carbon directly. The presence of spectator cations (M ⁿ⁺) enhances the formation of M ⁿ⁺{Au(CN) ₂ ⁻ } _n ion pairs on the carbon, which in turn suppress the elution of gold cyanide. The dynamics of removal of these cations determine the horizontal position of the gold peak in an elution profile. When the concentration of cations in the eluant is high and no cyanide is present in the solution or on the carbon, very little desorption of gold is observed. The quantitative effect of the concentration of spectator cations on the equilibrium for desorption of aurocyanide can be estimated from the elution profiles for gold and cations. Free cyanide in the eluant, which causes some competitive adsorption of cyanide with aurocyanide, therefore plays a minor role at the elevated temperatures used in industry. A more important effect of cyanide is its reaction with functional groups on the carbon, the products of which passivate the surface for adsorption of aurocyanide, and thereby cyanide promotes the elution of aurocyanide. The degree of passivation, which is determined to a large extent by the temperature of pretreatment, also affects the elution of cations and the degradation/adsorption of cyanide itself. Reactivation of the carbon surface occurs when the adsorbed/decomposed cyanide is removed by the eluant. At high temperatures of pretreatment, such as used in practice, it is not necessary to include a reactivation term in the mathematical model for elution.     

Models for the adsorption of aurocyanide onto activated carbon. Part I: Solvent extraction of aurocyanide ion pairs by 1-pentanol

Factors influencing the adsorption of gold cyanide onto activated carbon are well known, but there is currently no consensus of opinion on the actual mechanism of extraction. This situation has arisen mainly because activated carbon is not readily amenable to conventional techniques of chemical investigation such as infrared and ultraviolet-visible spectroscopy. This study reports on a novel approach using a model system in which the analogous behaviour of the extraction of gold cyanide by ion-pair solvent extraction is demonstrated. The effect of the nature of the cation on gold extraction by activated carbon is explained in terms of the type of ion pair, viz., [Mⁿ⁺][Au(CN)₂⁻]_n, formed between the Au(CN)₂⁻ anion and the cation Mⁿ⁺ present in the adsorption medium.     

硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜

建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法。探讨了硫氰酸铵溶液用量、十四烷基三甲基溴化铵（TTMAB）溶液用量和酸度等因素对Cu²⁺浮选率的影响,讨论了Cu²⁺的浮选分离机理。结果表明,在最佳条件下,由Cu²⁺,SCN^-和十四烷基三甲基溴化铵阳离子(TTMAB⁺)形成的不溶于水的三元缔合物(TTMAB)₂ ［Cu(SCN)₄］被定量吸附在TTMAB⁺与SCN^-作用产生的微晶物质TTMAB⁺·SCN^-表面,且被浮选至水相上形成界面清晰的液-固两相,而Fe³⁺、Co²⁺、Ni²⁺、Cd²⁺、Mn²⁺、Al³⁺等离子仍然留在水相中,实现了Cu²⁺与这些离子的定量分离。据此建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法,进行了合成水样中Cu²⁺的定量浮选分离,浮选率为93.4%～103.6%。     

Potentiometric studies on the adsorption of Au(CN)2 and Ag(CN)2 onto activated carbon

The adsorption of Au(CN) ₂ ⁻ and Ag(CN) ₂ ⁻ onto activated carbon has been correlated with potential measurements of carbon. It is proposed that Au(CN) ₂ ⁻ , Ag(CN) ₂ ⁻ , and CN⁻ are adsorbed on carbon by both an ion exchange mechanism and an oxidative reaction which leads to a decrease in carbon potential. The potential of carbon decreased according to the degree of anion adsorption in the order Au(CN) ₂ ⁻ > Ag(CN) ₂ ⁻ > CN⁻ > I⁻ > Cl⁻. Adsorption of anions is accompanied by release of OH⁻ ion which raises the solution pH and decreases the carbon potential. The potential of carbon in contact with solutions containing KAu(CN)₂, KAg(CN)₂, or KCN is much more negative than that in contact with chloride solution at the same pH. The results indicate that cyanide is oxidized on the carbon surface by oxygen or by reducible functional groups such as quinone. N. TSUCHIDA, formerly Postgraduate Student, Murdoch University, is Metallurgist with Beshi Nickel Refinery (Sumitomo Metal and Mining Co.), Niihama, Japan     

Models for the adsorption of aurocyanide onto activated carbon. Part II: Extraction of aurocyanide ion pairs by polymeric adsorbents

The adsorption of aurocyanide onto activated carbon has been known but not fully understood for many years. This is due to the difficulty involved in studying the nature of the adsorbed gold cyanide species on activated carbon by conventional techniques of chemical investigation such as infrared and ultraviolet-visible spectroscopy. A novel approach using model systems was adopted by the authors to shed further light on the adsorption mechanism. This study reports on the extraction of gold cyanide by polymeric adsorbents and ion-exchange resins and demonstrates that, as in the case of ion-pair solvent extraction (Part I), the adsorptive behaviour of Au(CN)₂⁻ in the presence of various cations onto polymeric adsorbents is analogous to the adsorptive behaviour onto activated carbon (Part III). The effect of the cation is rationalized in terms of the type of ion pair viz., [Mⁿ⁺] [Au(CN)₂⁻]_n formed between the Au(CN)₂⁻ anion and the Mⁿ⁺ cation in the adsorption medium, and which is subsequently adsorbed.     

Removal of lead from aqueous solutions by natural phosphate

The removal of lead ions from aqueous solution was studied in batch experiments using natural phosphate (NP). The effects of initial concentration of lead and initial pH of solution were investigated and the mechanism for removal of lead has been suggested. The data obtained from sorption isotherms at different temperatures conformed to the linear form of the Langmuir adsorption equation. The influence of NO₃⁻ and Cl⁻ anions has been evaluated. The effect of varying levels of Cl⁻ has significant influence on the sorption capacity of Pb²⁺, while NO₃⁻ did not. The abundance of natural phosphate, its low price and non-aggressive nature towards the environment are advantages for its utilization in point of view of wastewater and wastes clean up.     

Models for the adsorption of aurocyanide onto activated carbon. Part III: Comparison between the extraction of aurocyanide by activated carbon,polymeric adsorbents and 1-pentanol

The factors that influence the adsorption of aurocyanide onto activated carbon, such as cation type, are examined, and compared with previous work using the model systems of 1-pentanol and polymeric adsorbent resins. The effect of the nature of the cation is rationalized in terms of the type of ion pair viz., [Mⁿ⁺] [Au(CN)₂⁻]_n, formed between the Au (CN)₂⁻ anion and the Mⁿ⁺ cation in the adsorption medium, and subsequently adsorbed onto the carbon surface. In a study of pyrolysed polymeric adsorbents, the temperature of activation is confirmed to have a profound influence on the adsorption of aurocyanide. X-ray diffractometry shows this to be related to the formation of a graphitic-type structure with a preponderance of micropores. The mechanism of adsorption is further clarified by E.S.R. spectroscopy, which indicates that a specific interaction between the adsorbed ion pair and the condensed aromatic structure is also probably occurring.     

酶催化分光荧光法测定环境水中痕量铬(Ⅵ)

铬（Ⅳ）对血红蛋白模拟酶催化荧光体系具有强烈的猝灭作用, 据此建立了一种酶催化分光荧光法测定铬（Ⅳ）的新方法。研究了溶液酸度、L-酪氨酸浓度、血红蛋白浓度、H₂O₂浓度及反应时间等因素对体系的影响。在pH10.4的NH₃·H₂O-NH₄Cl缓冲溶液中, 当L-酪氨酸、血红蛋白和H₂O₂的浓度分别为1.4×10^-4mol/L、1.0×10^-6mol/L和3.5×10^-5mol/L时, 测定铬（Ⅳ）的线性范围为2.0×10^-6～1.0×10^-4mol/L, 检出限为1.1×10^-8mol/L。1000倍NO₃^-、SO₄^2-、Na⁺、K⁺、Cl^-、Br^-, 300倍PO₄^3-、Al³⁺、NH₄⁺, 50倍Mn²⁺、Mg²⁺、Fe²⁺、Cu²⁺, 1倍Fe³⁺对铬（Ⅳ）的测定没有干扰。干扰较大的Fe³⁺, 可加入过量的柠檬酸掩蔽。对浓度为4.8×10^-5mol/L的铬（Ⅳ）进行11次平行测定, 其相对标准偏差为2.8%。该法已成功地应用于环境水样中铬（Ⅳ）含量的测定。     

Effect of Electrolysis and Heat Treatment Conditions on the Rate of Formation and Magnetic Properties of Very Fine Iron

The effect of electrolysis and heat treatment conditions on the rate of formation and magnetic properties of very fine iron cobalt alloy powder is studied. The optimum conditions for powder preparation are as follows: electrolysis temperature 70°C, heat treatment temperature 500°C, cathode rotation rate 1 rad/sec, cathode current density 2 kA/m², pH = 3.5 ± 0.5, oleic acid concentration 10 kg/m³, electrolyte concentration 20-30 kg/m³, ion ratios of 54:46 and 40:60 for Fe²⁺:Co²⁺.     

基于Freundlich吸附等温方程测定氰化提金工艺用活性炭的吸附金容量

活性炭作为金的良好吸附剂广泛地应用在氰化提金生产工艺中,因此对活性炭吸附金性能的评价是非常重要的。在参考氰化提金生产工艺的基础上,模拟活性炭吸附氰化液中金的工艺过程,基于Freundlich吸附等温方程,建立活性炭吸附金容量的测定方法。通过考察一系列对吸附金容量测定的影响因素,优化和确定了测定方法的条件:吸附振荡时间为16h,吸附溶液体积为150mL,活性炭粒度在0.074mm以下,振荡器转速为200r/min,吸附溶液pH值为11.5,振荡温度为(30±1)℃,吸附溶液中氰化钠质量浓度为0.2g/L。按照实验方法测定了2个活性炭实际样品的吸附金容量,结果的相对标准偏差(RSD,n=11)分别为4.2%和4.8%。并对不同活性炭的吸附金容量情况与碘值进行对比,结果表明实验方法具有可比性。     

基于Freundlich吸附等温方程测定氰化提金工艺用活性炭的吸附金容量

活性炭作为金的良好吸附剂广泛地应用在氰化提金生产工艺中,因此对活性炭吸附金性能的评价是非常重要的。在参考氰化提金生产工艺的基础上,模拟活性炭吸附氰化液中金的工艺过程,基于Freundlich吸附等温方程,建立活性炭吸附金容量的测定方法。通过考察一系列对吸附金容量测定的影响因素,优化和确定了测定方法的条件:吸附振荡时间为16h,吸附溶液体积为150mL,活性炭粒度在0.074mm以下,振荡器转速为200r/min,吸附溶液pH值为11.5,振荡温度为(30±1)℃,吸附溶液中氰化钠质量浓度为0.2g/L。按照实验方法测定了2个活性炭实际样品的吸附金容量,结果的相对标准偏差(RSD,n=11)分别为4.2%和4.8%。并对不同活性炭的吸附金容量情况与碘值进行对比,结果表明实验方法具有可比性。     

Gold recovery from non-metallic secondary raw materials by leaching with thiourea and adsorption on ion exchangers

Elemental gold on non-metallic secondary raw materials is easy to dissolve by leaching with sulphuric acid solutions of thiourea in the presence of an oxidant such as iron(III) sulphate or hydrogen peroxide. Leaching time is highly dependent upon oxidant concentration and the thickness of the gold coating. The gold goes into solution as the Au[SC(NH₂)₂]_2⁺ complex and can be removed almost completely using cationites, the gold residues being not greater than 6 μM. The gold-free leaching solution may be reused for leaching; the completely-loaded cationite resin (with a gold content of about 30–60 g/l) is burnt to recover the gold.A study of the adsorption of Au and Fe by cationites indicates that the adsorption of gold takes place purely by means of an ion-exchange mechanism, the bond of the gold complex being considerably stronger than that of the iron compounds.     

The mechanism of adsorption of aurocyanide onto activated carbon

The mechanism of adsorption of aurocyanide onto activated carbon and its subsequent élution are examined in this study, with special reference to the effects of acid and alkali treatment on the system. The results, including a careful analysis of the distribution of all ions in the ad-sorption and elution processes, are discussed, and evidence for the adsorption and elution mech-anisms involved is presented. It is proposed that, under normal plant conditions, aurocyanide is extracted onto activated carbon in the form of an ion pair, Mⁿ+[Au(CN)₂]ⁿ], and eluted by hydroxide or cyanide. The hydroxide or cyanide ions react with the carbon surface, rendering it relatively hydrophilic with a decreased affinity for neutral species. Additional adsorption mechanisms are shown to operate under other conditions of ionic strength, pH, and temperature, and it is suggested that this may account in part for the lack of agreement among workers.     

Studies on role of oxygen in the adsorption of Au(CN) 2 − and Ag(CN) 2 − onto activated carbon

Comparative studies of the adsorption of Au(CN) ₂ ⁻ , Ag(CN) ₂ ⁻ , and Hg(CN) ₂ ⁻ onto activated carbon (Norit R2020) have suggested that oxygen and oxygen containing surface functional groups play a role in the adsorption process of Au(CN) ₂ ⁻ and Ag(CN) ₂ ⁻ but not in the adsorption of Hg(CN) ₂ ⁻ . Adsorption of Au(CN) ₂ ⁻ and Ag(CN) ₂ ⁻ on carbon degassed at 950 °C under 10⁻⁵ torr (1.33 × 10⁻³ P) vacuum is decreased by 50 pct compared with the adsorption on normal activated carbon. However, in the presence of oxygen in solution, the degassed carbon adsorbs Au(CCN) ₂ ⁻ to the same extent as normal carbon. The effect of organic solvents and the variation in the potential of the two types of carbon upon adsorption of Au(CN) ₂ ⁻ were also investigated. These results indicate that activated carbon behaves like an ion-exchange resin but is capable of oxidizing cyanide and cyanide complexes by chemisorbed oxygen. A dual mechanism for the adsorption of Au(CN) ₂ ⁻ and Ag(CN) ₂ ⁻ onto activated carbon is therefore proposed, in which cyanide complexes adsorb on carbon by anion exchange with OH⁻ followed by partial oxidative decomposition of Au(CN) ₂ ⁻ or Ag(CN) ₂ ⁻ to insoluble AuCN or AgCN. N. TSUCHIDA, formerly Postgraduate Student at Murdoch University,     

矿石中金的溴氧化浸出的热力学分析

根据“物料平衡”与”同时平衡”的原理,对矿石中金的溴氧化浸出体系进行了热力学分析,构成其电位-pH 图。由电位-pH 图推测了金离子浓度,溴离子浓度以及温度的变化对平衡电位的影响。随着矿石中金的浸出,溶液中金离子的浓度增大,金-溶液的平衡电位随之升高,金离子的水解pH 值减小,溶液的稳定区减小;反之,增加溶液中溴离子的浓度,则能降低金-溶液的平衡电位,增大金离子的水解pH值,扩大溶液的稳定区;升高浸金溶液的温度,同样能扩大溶液的稳定区,有利于金的浸出。     

Synthesis of 4-acylpyrazolone Schiff base ligand grafted silica and selectivity in adsorption of lanthanides from aqueous solutions

The Schiff base form of the 4-acylpyrazoione ligand was immobilized on the silica surface by reaction of 3-aminopropyl silica with 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one in 97% yield, producing grafted silica with 0.77 mmol/g ligand loading. This surface modified silica was shown to be selective in the adsorption of Yb3+ ions from dilute aqueous solutions, for which 98% adsorption was observed from a 1.0×10-5 mol/L aq. solution at pH 6.7, after 24 h at room temperature. Six other lanthanides studied Eu3+, Gd3+, Nd3+, Tb3+,Sm3+ and La3+ showed moderate to weaker adsorptions of 39%, 28%, 16%, 12%, 11% and 5% respectively under similar conditions.