Evaluation of ecological risk and primary empirical research on heavy metals in polluted soil over Xiaoqinling gold mining region,Shaanxi,China

Soil,crop and residents'hair over Xiaoqinling gold mining region,China,which was selected as a case study,were sampled and analyzed for Hg,Cd,Pb,Cu,Cr,As and Zn concentrations.The concentrations of heavy metals in soil or crop and hair samples were used to assess their potential ecological risks,or to find the responses to these metals as evidences to prove the potential risk was coming down to observed harm,respectively.The results showed that,these metals in soil were ranked by severity of ecological risk as Hg>Cd>Pb>Cu>Cr>As>Zn,based on their single-element indexes.In the view of the potential ecological risk indexes,of all soil samples,about half had significantly high or high potential ecological risk,which covered more than 74%of the studied region.Most of the risks were 97.41%from Hg,Pb and Cd,especially,84.37%from Hg.Both the single-element and potential ecological risk indexes indicated that,the ecological risk grades had a special spatial characteristic,and increased from northwest to southeast generally.This was agreed with the spatial distribution of the strength in gold mining activities over the studied region.The concentrations of Hg and Pb were higher than their relative backgrounds in the corps,and were even 9.48 and 25.09 times higher than their relative backgrounds in residents'hair,respectively.All these showed that the heavy metals in the soil had a high potential ecological risk,especially,had been affecting these crops'growing and yield,and even the residents'health through food strains.Obviously,these metals'potential ecological harm had been coming down to observed harm to the ecology.

Adsorption and Desorption of Gold on the Magnetic Activated Carbon

Adsorption and desorption of gold on the magnetic activated carbon (MAC) were investigated The adsorption rate of gold is higher than that of conventional coconut carbon in cyanide leach solution The loading gold can be easily desorbed as coconut carbon. Crushed fine magnetic carbon can be selected by a magnetic separator, It is suggested that the MAC can be used in carbon-in-pulp (CIP)process for increasing the recovery rate of gold

Non-metallic gold nanoclusters for oxygen activation and aerobic oxidation

In recent decade, Au nanoclusters of atomic precision （AunLm, where L= organic ligand： thiolate andphosphine） have been shown as a new promising nanogold catalyst. The well-defined AunLm catalystspossess unique electronic properties and frameworks, providing an excellent opportunity to correlate theintrinsic catalytic behavior with the cluster＇s framework as well as to study the catalytic mechanismsover gold nanoclusters. In this review, we only demonstrate the important roles of the gold nanoclustersin the oxygen activation （e.g., 302 to 102） and their selective oxidations in the presence of oxygen （e.g., COto C02, sulfides to sulfoxides, alcohol to aldehyde, styrene to styrene epoxide, amines to imines, andglucose to gluconic acid）. The size-specificity （Au25 （1.3 nm）, Au38 （].5 nm）, Au144 （1.9 nm）, etc.）, ligandengineering （e.g., aromatic vs aliphatic）, and doping effects （e.g., copper, silver, palladium, and platinum）are discussed in details. Finally, the proposed reactions＇ mechanism and the relationships of clusters＇structure and activity at the atomic level also are presented.

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.