| With the fast development of gold mining, dressing and smelting technologies, the scope of gold resources is constantly and rapidly expanding, from simple and easy resources to hard-to-process ones. Among the hard-to-process gold resources, arsenic sulfide gold ore has the most reserves and the highest recycling value, and thus it has received closed attention recently. Arsenic (As), due to its highly-toxic potential that may cause defection, cancer and deformation, arouses widespread public concerns. The arsenic in gold ores not only impairs cyanide leaching rate but also contaminates the air, water and soil. Therefore, it is essential to exclude the arsenic from the hard-to-process gold ores. Thanks to the development of phytoremediation and the discovery of As-hyperaccumulators, such as Pteris vittata L., Pteris cretica L., it has become possible to remediate As-contaminated soil and water with the economical, effective and environmentally-friendly method. These As-hyperaccumulators can also be used to remove the arsenic from arsenic-bearing gold ores.A field survey was conducted to screen potential As hyperaccumulators and evaluate current As contamination of soil and plants in arsenic-gold-ore mine areas in Yunnan and Guizhou Provinces. The results showed that Xingren arsenic gold mine of Guizhou province has higher concentrations of arsenic and gold than those in other investigated area, and further arsenic removal is needed using arsenic hyperaccumulators. In subsequent research, the direct-leaching experiments was conducted using arsenic gold ore to find the efficient As activate agents. The As hyperaccumulator, Pteris vittata L. is widely distributed in the research area. In the following pot experiments, Pteris vittata L. was planted in arsenic-containing gold ore which was smashed and passed through a filter of<0.037mm mesh. Different agents were added to improve the arsenic removal efficiency of Pteris vittata L. The As forms in the arsenic-containing gold ore were studied under different leaching agents treatment and root-exudation.The results showed that:1) In Southwestern China, riched arsenic-gold-ore mineral resources were found. Mineral samples were collected and concentrations of Au and As were measured from Weisha gold mine(WS), Guanting gold mine(GT), Puxiong gold mine(PX) and Xingren gold mine(XR). Based on the data of soil and mineral survey around these four gold mine areas, the concentrations of As in the soils were much higher than those in red earth of China (average19.85mg/kg). Moreover, it was far beyond the third class standard (≤40mg/kg) in dryland according to Environmental Quality Standard for Soils in China (GB15618-1995). The soils in these investigated areas were heavily contaminated by As to some extent. The unqualified rate of soil As was100%, far exceeding the recommended Environmental Quality Standard for Soils mentioned above, with exceeding times from6.45to89.85. The soil was heavilly polluted by As around tailings dam, and further recovering is needed. Trace amounts of gold residue were also determined from the arsenic-containing gold-ore mine tailing. It will be difficult to yield gold by cyanidation leaching from mine tailing for industrial value. Therefore, it is necessary to find a new technique, such as phytoremediation, to recover and reuse gold resisue effectively.2) Arsenic concentrations varied greatly in plants growing in the investigated areas. Arsenic concentrations in stems and leaves were relatively high in some species except previously reported arsenic hyper-accumulators, such as P. vittata and P. cretica. The translocation factor of Aster subulatus, Buddleia officinalis, Amaranthus tricolor, Anaphalis margaritacea and Polygonum nepalense was higher than6. They could serve as potential As hyper-accumulators to remediate As pollution in soil. In addition, As concentrations in edible parts of crops (except Zea mays L.) and other wild edible plant greatly exceeded the standard for food safety of China. All of the plants in present study were naturally collected from the old mine areas, and their As concentrations exceeded the maximum tolerance concentrations. Prevention of soil As pollution must be studied systematically to guarantee food safety.3) Mineral samples of above four gold mine were collected to determined Au and As concentrations. Results showed that only Xingren gold mine in Guizhou Province met our demand for present research. Au and As concentrations were3.8mg/kg and8500mg/kg in Xingren gold mine, respectively. X-ray diffraction (XRD) analysis indicated that the mineral samples consisted of complicated materials. Major metallic minerals in samples included pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, stibnite (antimonite), native Sb (stibnite), tetrahedrite, hematite, limonite, scorodite, chalcocite, and some precious metal materials such as native gold, silver-gold mineral, nature silver and argentite. Gangue minerals was mainly calcite, muscovite, quartz, dolomite and other minerals such as feldspar. We used some methods to study the main gold-bearing minerals of Xingren(Zimudan) gold deposit, including panning, chemical analysis, X-ray diffraction analysis, microprobe analysis etc. The gold mineral was mainly native gold and little silver-gold mineral. Other gold mineral and gold-bearing minerals was not found. One part of gold was lied in pyrite and arsenopyrite as independent minerals such as native gold. The gold was mainly existed as microparticles in pyrite and arsenopyrite, but arsenic mainly existed in arsenopyrite.4) Ionic As concentrations were negligible in Xingren gold ore with a ratio of0.05%, but residual fraction was up to81.94%. Arsenic availability was extremely low in investigated gold mineral samples. Shocking and leaching experimental study were conducted by ethylenediaminetetraacetic acid disodium salt (EDTA-Na2), monoammonium phosphate (NH4H2PO4,MAP), sodium bisulfite (NaHSO3), sodium bicarbonate (NaHCO3), monoammonium nitrate (NH4NO3), citric acid (C6H8O7,CA) and succinic acid (C4H6O4) with different concentrations and process time. A blank control group (CK) was leached by deionized water simultaneously. The sequentailly extracted experiments were designed to determine different As forms by ammonium chloride (NH4C1), ammonium fluoride (NH4F), sodium chloride (NaCl), sodium hydroxide (NaOH) and sulfuric acid (H2SO4). Results showed that available As including soluble As and ionic As increased obviously by adding different leaching agent except NH4NO3. Available As increased progressively with the extension of shocking time. Under the conditions of present experiment, maximum available As ratio increased to1%after leaching with high concentration of NH4H2PO4and CA(C6HgO7) after shocking3hours and20hours. Quasi-bound state As concentrations including Al-As, Fe-As and Ca-As varied differently with different shocking time. They increased with the extension of shocking time except NaHSO3treatment. Under the conditions of this experiment, maximum bounded-As ratio increased from19%to37%after leaching by high concentration of C6H8O7when shocking from1hour to20hours. According to activation ability of As from residual forms to available ones and taking energy-conserving into account, it was efficient to set the shocking time as3hours.5) Pot experiment showed that total quantity of As removal were siginificantly higher after leaching by MAP than other treatments. On the one hand, MAP can serve as fertilizer to promote the growth of P. vittata. On the other hand, MAP can compete adsorption sites from pyrite and clay minerals to activate available As concentration. Therefore, MAP increased As uptake of P. vittata. Citric acid increased the biomass of P. vittata. Different effect of other leaching agents and culture time (1month and3months) on P. vittata was observed. Pot experiment indicated that higher removal of As could be acquired by harvesting P. vittata every4months. P. vittata plants cultured in smashed materials could remove more As than those in middle size or coarse sand of the gold mineral samples, because it is easier for As expose in smashed materials.6) The concentrations of ionic As and combination forms (including Al-As, Fe-As and Ca-As) were improved obviously in rhizosphere and in non-rhizosphere when P.vittata plants were cultured in smashed arsenic-gold-ore. However, residual fraction As were reduced obviously in rhizosphere compared with non-rhizosphere. Results showed that P. vittata played an important role in As activation from residual fraction to Ca-As, Al-As and ion-As. It was shown that root exudants had obvious effects on arsenic activation from arsenic-containing gold-ore. The residual fraction of As in original ore was decreased by30%and20%after planting P. vittata for4months in rhizosphere and in non-rhizosphere, respectively. Secondly, the concentrations of ionic As and combination forms were improved obviously in rhizosphere compared with non-rhizosphere when planting P. vittata in smashed arsenic-gold-ore. The root exudants of P. vittata has an obvious effect on arsenic translocation from the roots to fronds. The results from XRD analysis indicated that the ore samples had the same mineral constituents but different concentrations after growing P. vittata for4months. Arsenopyrite was decreased by0.89%after planting P. vittata for4months, to be equivalent to As decreasing by0.41%.7) The gold recovery was34.21%by using direct cyanide leaching, but the rate increased by12%-18%after planting P. vittata in arsenic-containing gold-ore. Citric acid could improve the cyanidation leaching environment, increase the leaching speed and reduce the cyanidation leaching time and the cyanide consumption. Cyanide leaching of arsenic-containing gold-ore regulated by citric acid resulted in a gold recovery of52.24%. Gold recovery of cyanide leaching was significantly increased by adding ammonium dihydrogen phosphate, sodium bisulphate and citric acid compared with the non-planted or non-regulated original ore. The three agents has noticeable arsenic activation from arsenic gold ore and further experiments in large scale are needed.
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