ADSORPTION CAPACITY OF ACTIVATED CARBON FIBER FABRIC IN CYANIDE LEACHING LIQUOR OF GOLD ORES

1. INTRODUCTION Reclamation of gold in liquid of gold with activated carbon fiber (ACF) is reported. ACF possessed numerous advantages, such as high adsorption capacity, great adsorption rate and high recovery of gold. It was generally considered tha…     

Advantages and disadvantages of various kinds of adsorbents used in industrial extraction of [Au(CN)<Subscript>2</Subscript>]<Superscript>–</Superscript> anions from cyanide solutions and pulps

Comparative study of an industrially used activated carbon of WSC-207C-GR brand, strongly basic anion exchanger MINIX, and weakly basic anion exchanger Purogold S992 in recovery of [Au(CN)₂]^– ions from cyanide aqueous solutions and slurries was carried out. It was found that the strongly basic anion exchanger MINIX has the highest adsorption rate of the cyanide complex of gold(I), whereas the activated carbon and the weakly basic ion exchanger possess a substantially higher selectivity toward the complex of gold(I). Use of each of the three sorbents makes it possible to solve the problem of the cyanide leaching of gold from ores containing natural substances that exhibit adsorbent properties with respect to the dicyanoaurate(I) ion. The influence exerted by the amount of kerosene additive and volume fraction of a sorbent on the efficiency of gold recovery by the sorbent in cyanidation of ores in the “carbon-in-pulp” and “resin-in-pulp” modes.     

Anodic Dissolution of Gold in Alkali–Cyanide Solutions: Effect of Lead Ions

Effect of the presence and the concentration of lead ions on the anodic dissolution of gold in cyanide electrolytes is studied. The ions dramatically accelerate the process in the potential region extending from –0.61 V vs. NHE (equilibrium potential of gold) to –0.2 V. The effect is attributed to a catalytic action of adsorbed lead ions on the process.     

Gold recovery from cyanide solutions with a new fibrous polymer adsorbent

In a resin-in-pulp process for the recovery of gold cyanide from a very dilute solution it is desirable that the resin should exhibit the ability to load gold at the natural pH of the leach liquor and be stripped by an aqueous alkali. The present work describes the results of gold cyanide adsorption by new ion-exchange hollow fibers prepared by the amination of sulfochlorinated polyethylene. The fibers, chopped into suitably sized pieces, showed very fast adsorption and desorption of gold from mixed cyanide solutions.     

Extraction of Gold from ores and concentrates by leaching with the use of cyanides and alternative reagents

The problems associated with gold mining are considered from the standpoint of application of heap leaching, a method for gold recovery. Data on the kinetics and mechanism of gold dissolution in cyanide and alternative solvents [thiocarbamide solutions containing Fe(III) ions and hypochlorite-chloride bromine-bromide, iodine-iodide, and copper-thiosulfate solutions], which make it possible not only to improve the working efficiency in gold mining, but also to lessen the contamination of the environment with highly toxic compounds.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1585–1604.Original Russian Text Copyright © 2004 by Kozin, Melekhin.     

“Surface-enhanced Raman spectroscopy studies of the passive layer formation in gold leaching from thiosulfate solutions in the presence of cupric ion”

Complementary electrochemical and spectroscopic techniques were used to characterize the behavior and composition of the passive layer formed at the gold surface in a thiosulfate electrolyte in the presence of cupric ions. Raman studies of three different cationic (calcium, ammonium, and sodium) thiosulfate leaching solutions revealed that the concentrations of thiosulfate, trithionate, sulfate, and tetrathionate remained constant in the bulk solution over a 3-h time period. The initial leaching current densities of these three systems were identical; however, significant differences in the open circuit potentials of these systems were observed. To provide additional information about the nature of the passive layer, gold nanorod array electrodes were fabricated and employed as substrates for studying the species present at the gold–thiosulfate interface using surface-enhanced Raman spectroscopy (SERS). The composition and behavior of the passive layer at the gold–thiosulfate interface greatly differed from those of the bulk solutions. The passive layer consisted primarily of elemental sulfur and sulfide-like species, with thiosulfate and its oxidation products, such as tri- and tetrathionates, as minority components. The nature of the cation (calcium, sodium, or ammonium) of the thiosulfate salt showed no significant effect on the composition of the passive layer at leaching times longer than 100 min. In addition, the presence of cupric ions also had no significant effect on the formation of the passive layer. However, copper is a much better oxidant than oxygen in gold–thiosulfate leaching reactions.     

A label-free gold-nanoparticle-based SERS assay for direct cyanide detection at the parts-per-trillion level

Cyanide is an extremely toxic lethal poison known to humankind. Developing rapid, highly sensitive, and selective detection of cyanide from water samples is extremely essential for human life safety. Driven by the need, here we report a gold-nanoparticle-based label-free surface-enhanced Raman spectroscopy (SERS) system for highly toxic cyanide ion recognition in parts-per-trillion level and to examine gold-nanoparticle-cyanide interaction. We have shown that the SERS assay can be used to probe the gold nanoparticle dissociation process in the presence of cyanide ions. Our experimental data indicates that gold-nanoparticle-based SERS can detect cyanide from a water sample at the 110 ppt level with excellent discrimination against other common anions and cations. The results also show that the SERS probe can be used to detect cyanide from environmental samples.     

Control of gold nanoparticle aggregates by manipulation of interparticle interaction

The size of gold nanoparticle aggregates was controlled by manipulating the interparticle interaction. To manipulate the interparticle interaction of gold nanoparticles prepared by citrate reduction, we applied the substitutive adsorption of benzyl mercaptan on the particle surface in the absence of the cross-linking effect. Various experimental techniques such as UV-vis absorption spectroscopy, surface-enhanced Raman scattering, quasi-elastic light scattering, and zeta-potential measurement were used to characterize the nanoparticle aggregates. Our results suggest that the replacement of the trivalent citrate ions adsorbed on the nanoparticle surface with monovalent benzyl mercaptan ions should destabilize the particles, causing aggregation and hence the increase in the size of nanoparticle aggregates. These experimental results were successfully rationalized by the classical DLVO (Derjaguin-Landau-Vervey-Overbeek) theory that describes the interparticle interaction and colloidal stability in solution. Our findings suggest that the control of surface potential is crucial in the design of stable gold nanoparticle aggregates.     

黄金矿的催化浸取

基于对金自溶解电化学过程的分析，提出此过程受阴极还原反应所控制，加入阴极反应催化剂，能加快金自溶速度，实验结果充分表明，我们找到的催化剂Ａ能提高金的浸出速度和浸出效率。     

纳米金膜电极上CN~-吸附的电化学和原位红外反射光谱研究

应用循环伏安(CV)和原位红外反射光谱(in situFTIRS)研究碱性介质中氰(CN-)在纳米金膜电极(nm-Au/GC)上的吸附行为.结果显示,当研究电极电位低于0.0 V时,CN-可稳定吸附在nm-Au/GC电极表面,高于0.0 V,则发生氧化脱附.发现nm-Au/GC表面具有异常红外效应(AIREs),即吸附态CN-谱峰呈现出与本体Au电极不同的方向倒反、红外吸收增强(39.2倍)以及半峰宽增加的异常光谱特征.本研究将纳米薄膜材料的这一AIREs从过渡金属拓展到币族金属,进一步证明AIREs是迄今研究的金属及合金纳米材料的普遍特性.     

活性碳纤维对银离子还原吸附能力的改进

活性碳纤维不仅对有机物有高的吸附容量,对贵金属离子也具有强的还原吸附能力,可将Pd(Ⅱ）,Ag（Ⅰ）,Au（Ⅲ）等离子还原为金属单质。因而可用于提取矿液或加收废液中的贵金属。由此,提高或改善贵金属在活性碳纤维上的还原吸附容量或分布形成,显得非常重要。本文研究了活性碳纤维制备条件、表面氧化改性、以有负载有机物等对活性碳纤维还原能力的影响。结果表明,（1）制备条件对剑麻基活性碳纤维的还原能力有很大的影响。用H3PO4或ZnCl2活化的活性碳纤维对银离子具有更高的还原吸附容量,分别可达250和700mg/g,约为水蒸汽活化剑麻基活性碳纤维对银离子还原吸附容量的2倍和5倍。（2）过氧化氢、高锰酸钾、或硝酸等无机氧化剂对活性碳纤维进行表面改性,也能提高活性碳纤维的还原能力。结果表明,虽然改性活性碳纤维的比表面积和孔体积下降10-20%左右,但基表面含氧量及含氧基团的种类发生了改变。这些改性活性碳纤维对Ag(NH3)2^ 的还原吸附量大幅度提高,可达550mg/g以上。推断表面改性在活性碳纤维表面创造了更多有利于碱性条件下发生氧化还原的活性点。（3）在活性碳纤维表面负载适当的有机物如亚甲基蓝、苯胺或对硝基苯酚,也能显著提高活性碳纤维对Ag(NH3)2^ 的还原吸附能力。     

Electrocatalysis by adatoms at the gold and silver dissolution in cyanide solutions

The peculiarities of the effects of upd thallium, lead, bismuth, and mercury on the dissolution rates of gold and silver in cyanide electrolytes are compared. In general, they feature the abrupt acceleration of the dissolution of gold and, to a lesser extend, silver in the chemisorption range of mentioned ions. As the potential increases, the gold dissolution rates passes through a maximum the height of which is comparable with the limiting current of this process associated with limitations in the delivery of cyanide ions to the electrode surface. The current decay after the maximum is due to desorption of catalytically active adatoms. The chemisorption rate of thallium, lead, and bismuth ions at potentials more negative than the current peak is controlled by their diffusion to the gold surface, whereas the chemisorption rate of mercury is controlled by the adsorption kinetics. With the increase in the surface coverage with adatoms θ, the catalytic activity of all considered adatoms passes through a maximum. The sharp increase in the effective transfer coefficient in the presence of these adatoms makes the main contribution into the acceleration of the gold dissolution, while the increase in the exchange current has a smaller effect. The chemisorption of mentioned atoms on gold not only accelerates the dissolution but also changes its mechanism. For gold dissolution, the catalytic activity of upd thallium, lead, and bismuth increases in the following sequence: Tl ? Pb < Bi and the effect is additive in their simultaneous presence. For silver, the increase in the exchange current makes the main contribution into the acceleration of dissolution, whereas the transfer coefficient and the reaction order with respect to the ligand change insignificantly. Explanation of the observed peculiarities is given.     

蒸馏分离-电感耦合等离子体原子发射光谱法测定氰化样品中砷的含量

砷是黄金选冶过程中常见的元素之一,选冶过程中砷的存在在一定的程度上影响了黄金等贵金属的氰化浸出效果。选冶样品中砷含量的准确分析可以为黄金选冶提供可靠地数据,并且采用一定的方法避免选冶过程中砷存在的影响。本方法通过饱和溴水-硝酸-硝硫混酸强氧化剂处理含氰样品,一方面分解氰化物,另一方面将各种形式的砷氧化为五价离子;再通过加入溴化钠催化剂,用硫酸亚铁将五价砷还原为三价砷,在108℃条件下,通过蒸馏方式将三价砷蒸馏出来,利用电感耦合等离子体原子发射光谱仪测定砷的含量。通过实验得出本方法的检测限为0.0019%;方法的精密度RSD<2%;方法的准确度-加标回收实验范围为99.8%-100.9%;通过与溴酸盐滴定法之间对比,说明了结果的准确性是可靠地。     

BPR树脂对Au(Ⅰ)、Ag(Ⅰ)等氰合离子的离子交换与吸附研究(Ⅰ)——吸附、解吸动力学

考察了BPR树脂在碱性条件下对金的吸附性能。研究了BPR提取Au(Ⅰ)、Ag(Ⅰ)及其它金属氰合离子的单、双组分动力学传质过程。结果表明,树脂相上氰合离子的传质速率和摩尔比与其结构类型有密切的关系,对Au(Ⅰ)等氰合离子的NH₄SCN解吸动力学作了系统的考察。     

城市生活垃圾焚烧飞灰重金属的浸出特性

对用流化床焚烧炉混烧垃圾和煤的布袋飞灰进行了重金属的TCLP(Toxicity Characteristic Leaching Procedure)浸出特性实验，探讨了液固比、初始pH值及浸出时间对飞灰中重金属Pb、Cr、Cd、Ni、Cu、Zn的浸出影响。结果表明，重金属的浸出量都随着液固比的增加而增加，其中Cr、Cu一般呈上升趋势，Cd、Ni、Zn在液固比大于20时曲线变化较平缓，Pb的浸出规律比较特殊，有一个明显的波峰和波谷。重金属在浸取液的pH≤2.90时的浸出浓度远远大于pH≥4.03时的浸出浓度。Pb、Cr、Zn随着浸出时间的增加，浸出浓度下降，而Cd、Ni上升，Cu是先上升后下降。在液固比、初始pH值及浸出时间这三个影响因素中，pH值对重金属的浸出影响较大，重金属在酸性环境下较易浸出。     

Bioleaching of UO22+ Ions from Poor Uranium Ores by Means of Cyanobacteria

The present paper deals with the study on uranium (VI) leaching, as uranyl ions, from ores with a poor content in util minerals, using some algae as: Porphyridium cruentum (Smith and Soerly) Nägeli, Spirulina platensis CNM-CB-02 and Nostoc linkia (Roth) Born and Flah. The basic composition of these ores allowed the self-maintenance and self-development of these microorganisms, which have facilitated then the leaching of the uranium (VI) as UO₂ ²⁺ ions. The microbial leaching degree was comprised between 40–90%, depending on the used alga and experimental conditions.     

Surface-enhanced vibrational spectroscopy of B vitamins: what is the effect of SERS-active metals used?

Surface-enhanced Raman scattering (SERS) spectroscopy and surface-enhanced infrared absorption (SEIRA) spectroscopy are analytical tools suitable for the detection of small amounts of various analytes adsorbed on metal surfaces. During recent years, these two spectroscopic methods have become increasingly important in the investigation of adsorption of biomolecules and pharmaceuticals on nanostructured metal surfaces. In this work, the adsorption of B-group vitamins pyridoxine, nicotinic acid, folic acid and riboflavin at electrochemically prepared gold and silver substrates was investigated using Fourier transform SERS spectroscopy at an excitation wavelength of 1,064 nm. Gold and silver substrates were prepared by cathodic reduction on massive platinum targets. In the case of gold substrates, oxidation–reduction cycles were applied to increase the enhancement factor of the gold surface. The SERS spectra of riboflavin, nicotinic acid, folic acid and pyridoxine adsorbed on silver substrates differ significantly from SERS spectra of these B-group vitamins adsorbed on gold substrates. The analysis of near-infrared-excited SERS spectra reveals that each of B-group vitamin investigated interacts with the gold surface via a different mechanism of adsorption to that with the silver surface. In the case of riboflavin adsorbed on silver substrate, the interpretation of surface-enhanced infrared absorption (SEIRA) spectra was also helpful in investigation of the adsorption mechanism.     

含硫氮螯合树脂对金、银及某些贱金属氰化物吸附性能的研究

用ＩＣＰ－ＡＥＳ研究了含硫氮螯合树脂对碱性氰化溶液中金、银、铜、铁、锌等金属离子的吸附行为。结果表明,该树脂除定量吸附金、银的氰化物外,也吸附铜、锌、铁的氰化物;吸附在树脂上的银及其它贱金属离子可以用２％ＮａＣＮ定量解吸,用硫脲－硫酸溶液可顺利地将金从树脂上洗脱下来,由此可实现金与银等元素的分离。树脂重复使用性能良好。对该树脂吸附金属氰化物的机理进行了初步探讨。     

碱性介质中L-赖氨酸在纳米金膜电极上的吸附和氧化过程

采用原位红外反射光谱(in situ FTIRS)和循环伏安法(CV)研究了碱性介质中L-赖氨酸在纳米金膜电极(nm-Au/GC)上的解离吸附和氧化过程. 研究结果表明, 在碱性溶液中以阴离子形式存在的赖氨酸[-OOC—CH—NH2—(CH2)4—NH2]在低电位区间(-0.95~-0.80 V, vs. SCE)发生部分解离, 生成AuCN-物种(约2110 cm-1), 同时赖氨酸阴离子的羧基侧还可通过两个氧原子与金电极表面相互作用. 随着电位的升高, 吸附态CN-氧化产生NCO-, OCN-和AuCN, 其对应的红外吸收峰分别位于2254, 2168和2226 cm-1附近.     

Fourier transform SERS studies of the chemisorption of ferricyanide on gold electrode surfaces

Surface enhanced Raman spectroscopy (SERS) studies of ferricyanide and ferrocyanide ions at gold electrodes show that in solutions containing 0.1 M Cs⁺, ferricyanide ions are adsorbed, but not ferrocyanide. The strength of the interaction with the surface is such that the electrode can be removed from the solution without loss of the SERS signal. This chemisorbed layer is also observed from solutions containing Li⁺ ions. The implications for the mechanism of the heterogeneous electron transfer reaction are discussed.