【作者】 王海娟；

【导师】 宁平；

【作者基本信息】 昆明理工大学 ， 环境工程， 2012， 博士

【摘要】 随着金矿大规模的开采和黄金选冶技术的发展,黄金资源开发的范围不断扩展,从性质单一的易处理黄金资源,迅速发展到难处理金矿资源领域。含砷金矿是难处理金矿石中储量最大、回收经济价值最高的金矿类型,也是目前研究最多的矿石类型。由于砷(As)的毒性和致畸、致癌、致突变效应,长期以来砷已成为公众普遍关注的环境污染物之一。金矿中砷的存在不但影响金的浸出,同时会造成大气、水体和土壤的环境污染,因此有必要对含砷难处理金矿进行除砷预处理。随着植物修复思想的提出、植物修复技术的发展以及蜈蚣草、大叶井口边草等砷超富集植物的发现,为砷污染土壤和水体的治理提供了更为经济有效和环境友好的方法,也为将其用于金矿除砷奠定了基础。本研究通过野外调查,对云南、贵州部分难处理金矿区矿物样品、周围土壤及植物进行了采样分析,评价了含砷金矿区造成的土壤和植物砷污染状况；选定了金、砷含量均较高的贵州兴仁金矿进行后续植物除砷的研究；利用研究区域内广泛分布的砷超积累植物蜈蚣草对难处理金矿进行了预处理；对金矿进行了直接淋洗活化,筛选有效促进砷淋溶的活化剂；以盆栽试验进行了调控处理,得到了有效的金矿除砷条件的调控方法；通过对金矿调控,分别提高了蜈蚣草砷去除效率及生物量；研究了淋洗剂及蜈蚣草根系分泌物对于金矿砷形态变化的影响。主要研究结果如下：1.本研究收集了云南省文山州渭砂金矿(WS)、红河州官厅金矿(GT)、普雄金矿(PX)和贵州兴仁县紫木魅金矿(XR)等矿物样品,通过对4个金矿尾矿区周围土壤调查分析表明,调查区域土壤中砷含量范围258.16-3594mg/kg,不仅远高于我国红壤中砷含量的平均值(约为19.85mg/kg),而且均超过GB15618-1995《土壤环境质量标准》中的砷含量旱地三级标准值。说明该有色金属矿区土壤超标率100%,超标倍数为6.45～89.85,土壤砷污染较严重,有待进行修复治理。另外,尾矿库有微量金残留,但是仅依靠氰化堆浸很难达到工业利用价值,因此有必要探索新的方法进行金的二次回收利用。2.植物调查结果表明,含砷金矿区周围植物砷含量变化较大,除已经公认的砷超积累植物蜈蚣草和大叶井口边草外,钻型紫菀、密蒙花、苋菜、珠光香青和尼泊尔蓼等几种植物地上部As积累量相对较高,转运系数均大于6。有望将其作为一种修复植物来治理土壤砷污染。另外分析表明,矿区周围栽种的部分农作物(除玉米未采集到种子)及野生的可食用植物,其可食部位砷含量均超标,有必要从食品安全的角度进行系统的研究和防治。3.通过对四个矿区金矿样品进行金、砷含量测定,筛选出金、砷含量均较高的兴仁金矿样品作为进一步植物除砷的目标。兴仁金矿矿石中的金元素的平均含量为3.8g/t,砷平均含量为0.85%。利用X衍射衍射分析(XRD)表明,兴仁金矿矿石中金属矿物组成较为复杂,所见金属矿物为：黄铁矿毒砂、闪锌矿、黄铜矿、方铅矿、赤铁矿、褐铁矿、臭葱石等,所见贵金属矿物包括自然金、银金矿石、自然银、辉银矿。矿石中脉石矿物组成主要是以碳酸盐矿物为主,其次为长石等其他矿物。通过鉴定发现金矿物在矿石中嵌布粒度呈现微细粒的特点,其中金主要以微细颗粒存在于黄铁矿和毒砂中,砷主要以毒砂形态存在。4.淋洗实验结果表明,金矿砷速效态(淋洗剂可溶态及离子态之和)含量极低,仅占原矿总砷的万分之五,而残渣态含量高,占总砷的81.94%。表明金矿砷有效性较低,通过用乙二胺四乙酸二钠、磷酸二氢铵、亚硫酸氢钠、碳酸氢钠、硝酸铵、柠檬酸和丁二酸7种试剂各3个浓度、3个时间梯度进行震荡、分级提取实验,结果表明,除硝酸铵外各试剂淋洗下速效态砷含量均有显著增加,并且有随着震荡时间延长而逐渐增加的趋势,在高浓度的磷酸二氢铵和柠檬酸作用下,震荡3h和20h后,速效态砷含量最大可以增加到1%以上。结合态砷含量(A1-As、Fe-As和Ca-As)在不同震荡时间下有不同变化趋势,但是除亚硫酸氢钠外,总结合态含量有随着震荡时间延长而增加的趋势,在高浓度柠檬酸作用下,从1h的19%分别增加到3h的33%和20h的37%。因此利用不同试剂进行金矿淋洗,可以把砷从残渣态向结合态和离子态逐渐活化,震荡淋洗时间从有效、节能的角度考虑以3h为佳。5.蜈蚣草调控试验结果表明,蜈蚣草吸收累积去除金矿砷的总量在磷酸二氢铵处理下有显著增加,表明磷酸二氢铵一方面起到肥料的作用,为金矿蜈蚣草生长添加了N、P肥,另外也对金矿砷的吸附-解吸起到竞争作用。通过磷酸二氢铵的加入,促进了砷从黄铁矿、粘土矿物等的解吸,提高了砷的有效性,从而促进了蜈蚣草对砷的累积。另外柠檬酸对生物量的增加起到了较明显的作用。其他试剂如EDTA-Na2、亚硫酸氢钠、碳酸氢钠和硝酸铵在蜈蚣草生长1个月和3个月时分别表现出不同的调控效果。蜈蚣草每生长3个月进行收割可以取得较高的除砷效率。在细磨矿样上种植蜈蚣草,有利于微细粒毒砂等砷化合物的暴露,从而去除效率比不同粒径配比的矿样高。6.根区砷形态分析试验结果表明,种植蜈蚣草后,与种植前的原矿相比,蜈蚣草根区、非根区的离子态砷含量、结合态砷含量均有明显提高,而残渣态砷含量则明显减少,表明植物对于残渣态砷向结合态砷转化、结合态砷向离子态转化有很大作用,蜈蚣草根系分泌物对于金矿砷活化有显著的作用。根区残渣态砷含量下降了近30%,而非根区残渣态砷含量下降了近20%。另外除Fe-As外,根区的离子态砷、Al-As、Ca-As均比非根区多,证明了蜈蚣草根系吸收营养和砷的同时对矿样中砷向根区移动有明显的作用。XRD定量分析结果也表明,种植蜈蚣草前后矿样的矿物组成基本相同,但矿物含量有所变化,矿物种植蜈蚣草前后毒砂减少了0.89%,相当于砷减少了0.41%。7.蜈蚣草预处理前后金氰化浸出试验结果表明,未经种植植物的原矿金浸出率最低,只有34.21%,而种植蜈蚣草4个月后的矿样金浸出效率均有所提高,其中利用柠檬酸调控的蜈蚣草处理后矿样金浸出效率最高,可以提高到52.54%。与未种植蜈蚣草的原矿以及种植蜈蚣草的对照(即未加调控剂)相比,利用磷酸二氢铵、亚硫酸氢钠和柠檬酸调控蜈蚣草除砷后金浸出效率也有显著提高。表明利用这三种试剂调控进行蜈蚣草除砷后对于金的浸提有明显效果。本论文成果通过植物预处理方法代替传统的火法焙烧预处理工艺,在提高金的浸出效率的同时,避免了传统工艺中因采用焙烧法除砷工艺给大气环境带来的砷污染,通过植物可以回收有价金属砷,有利于节能减排,对我国黄金选冶行业砷污染控制有推广应用价值。更多还原

【Abstract】 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.更多还原