Zinc and lead content and availability in Brazilian soil contaminated with residue of a secondary smelting lead recycling plant

The sequential extraction procedure of Zinc and lead performed in a Brazilian soil showed that it presents high pollution potential once over 90% of total lead is present in fractions where the metals can be easily mobilized. The fraction contents are as follow: F1 = 174 and 15 mg kg-1; F2 = 3155 and 9.7 mg kg -1; F3 = 99 and 1.6 mg kg -1; Residual fraction = 38 and 5.5 mg kg -1 for lead and zinc, respectively. The comparison with non contaminated soil only Pb 2+ concentration is above its intervention reference concentration, 900 mg kg -1.

Phase equilibria in the Fe-Zn-O system at conditions relevant to zinc sintering and smelting

Zincite and spinel phases are present in the complex slag systems encountered in zinc/lead sintering and zinc smelting processes. These phases form extensive solid solutions and are stable over a wide range of compositions, temperatures and oxygen partial pressures. Accurate information on the stability of these phases is required in order to develop thermodynamic models of these slag systems. Phase equilibria in the Fe–Zn–O system have been experimentally studied for a range of conditions, between 900°C and 1580°C and oxygen partial pressures (pO2) between air and metallic iron saturation, using equilibration and quenching techniques. The compositions of the phases were measured using Electron probe X-ray microanalysis (EPMA). The ferrous and ferric bulk iron concentrations were determined using a specially developed wet-chemical analysis procedure based on the use of ammonium metavanadate. XRD was used to confirm phase identification. A procedure was developed to overcome the problems associated with evaporation of zinc at low pO2 values and to ensure the achievement of equilibria. An isothermal section of the system FeO–Fe2O3–ZnO at high ZnO concentrations at 1200°C was constructed. The maximum solubilities of iron and zinc in zincite and spinel phases in equilibrium were determined at pO2 = 1 × 10-6 atm at 1200°C and 1300°C. The morphology of the zincite crystals sharply changes in air between 1200–1300°C from rounded to plate-like. This is shown to be associated with significant increase in total iron concentration, the additional iron being principally in the form of ferric iron. Calculations performed by FactSage with a thermodynamically optimised database have been compared with the experimental results.

中国炼锌向大气排汞及其环境影响的初步研究

汞是一种毒性极强的环境污染物。由于汞能在大气中存在并能长距离迁移，因此汞已经被定义为全球性污染物。研究表明有色金属锌的冶炼是大气汞的一个重要的人为汞污染源。西方发达国家在炼锌过程中由于有严格的污染物控制措施，使得这个问题得到有效的控制。由于经济和技术的原因我国大多数锌冶炼企业在冶炼过程中没有进行烟气汞的回收，从而使得我们不能借鉴国外的相关研究成果。我国2005年精锌总产量占到了世界的1/4，是全世界最大的锌锭生产国家，但相关的研究却非常滞后。近年来我国锌冶炼向大气排汞的问题已经引起了国际争议，而且冶炼过程中排放的汞对局部生态系统会产生重要影响，因此锌冶炼过程中释放汞所造成的环境问题已经越来越受到人们的关注和重视。 本研究的目的是通过对不同锌矿山的锌矿石和浮选锌精矿以及冶炼厂不同源锌精矿的研究从而了解我国的矿石汞含量，及矿石浮选过程中汞的分配；通过对冶炼过程向大气排汞的研究，认识锌精矿中汞在锌冶炼过程中的分配，估算不同冶炼方式汞的释放因子。如A、B和C冶炼厂是用不同的工艺来炼锌的，其汞的释放因子也不同。通过对土法炼锌区和工业炼锌区水体、土壤、大气和植物中汞的分布、迁移转化规律的研究，认识锌冶炼对局部生态系统产生的影响。 1.矿石和锌精矿中汞的研究 成因和分类不同的铅锌矿床锌矿石和浮选锌精矿中汞的测定结果表明：凡口矿的矿石和浮选的锌精矿中汞含量比兰坪矿矿石和浮选锌精矿高了2个数量级。凡口矿锌矿石和锌精矿中汞的含量分别是64.5-107 mg∙kg-1，588-602 mg∙kg-1；对应兰坪矿锌矿石和锌精矿中汞的含量分别是0.23~0.40 mg∙kg-1，1.91-3.33 mg∙kg-1。不同冶炼厂不同矿源的锌精矿中汞含量测定结果表明：不同源锌精矿中汞含量在0.10-1100 mg∙kg-1之间，变动范围非常大。而冶炼厂冶炼所用的混合锌精矿中汞含量差别不大，冶炼所用的混和锌精矿汞含量在37-105 mg∙kg-1之间变动。 2.锌精矿中汞在冶炼过程中的分配和汞释放因子的研究 对采用不同炼锌工艺的冶炼厂和有除汞工艺的A、B冶炼厂所用的锌精矿中的汞在冶炼过程分配的质量平衡对比表明，A冶炼厂和B冶炼厂锌精矿中的汞在冶炼过程中的分配显著不同，主要制约因素是是否对烟气中汞进行回收。在烟气到达除汞设备前，A和B冶炼厂在焙砂和尘、酸洗、电除雾等流程对烟气中汞的去除效果相近。不同的是，A厂要进行烟气汞回收，烟气经过汞回收后，50%以上烟气中的汞在这一流程被去除。这使得A、B冶炼厂后续的流程制酸吸收汞和排向大气汞所占的比例有较大的差异。 不同冶炼方式的汞释放因子表明，无任何环保措施的土法炼锌活动的释汞因子为113 g·t-1，不对烟气汞进行回收的B厂和C冶炼厂汞的释放因子分别为49 g·t-1和243 g·t-1，对烟气汞回收的A冶炼厂汞的释放因子为5.7 g·t-1。综合各种不同炼锌方式的汞释放因子及其精锌产量，得出了锌冶炼过程中汞的综合释放因子，从而估算出我国锌冶炼向大气排汞量约61.3-178 t·y-1。 3.锌冶炼对局部生态系统的影响 炼锌区的冶炼废渣是冶炼过程中的主要废弃物，随意堆放的废渣是当地农田土壤的重要汞污染源，大气汞中活性汞和颗粒态汞的沉降也是当地农田土壤另一个汞污染源。土法炼锌区和工业炼锌区土壤分析结果表明，工业炼锌对局部环境的影响更为严重。土壤汞含量对比如下：A冶炼厂周边环境污染土壤汞含量259-2990 μg·kg-1，远高于威宁土法炼锌点污染土壤汞含量72-355 μg·kg-1。威宁土法炼锌点土壤中甲基汞含量的分析表明，在冶炼点附近的土壤中甲基汞绝对含量和甲基汞/总汞的比例都高于其它样点，说明冶炼点附近土壤中汞的甲基化水平提高。A冶炼厂污水处理渣亦没有得到妥善的处理，成为当地潜在的汞污染源。 土法炼锌区水体汞的含量明显受到冶炼渣的影响。工业炼锌过程产生的废水经处理后的水汞含量100%超过国家工业废水排放标准，这些处理后的水的排放是当地重要的汞污染源。A冶炼厂周边稻田水分析表明，溶解态甲基汞占溶解态总汞的的平均比率（5%）远高于一般自然水体（<1%），可能与稻田特殊环境有关。 土法炼锌区大气汞含量测定表明，冶炼点附近大气汞浓度剧增，高达5220 ng·m-3，锌冶炼是当地主要的大气汞污染源。大气汞浓度的提升，是导致农作物玉米叶部位汞含量增高的原因。植物体的地上绿色部分通过叶片吸收大气汞是植物体内汞富集的重要途径之一。 土法炼锌区和工业炼锌区农作物果实中汞含量的测定结果对比如下：A冶炼厂附近稻田产出的部分大米样品中总汞含量已经超过了国家食品限量卫生标准（20 µg·kg-1），所有辣椒中总汞含量全部超出了国家蔬菜卫生限量标准（10 µg·kg-1）。土法炼锌区所取农作物样品未出现果实汞含量超标现象。食用这些汞含量超标的食物将对当地居民带来潜在的危害。

Copper and zinc stable isotope ratios as tracers of biogeochemical processes, sources and transport of Cu and Zn in soils

Copper and Zn are essential micronutrients for plants, animals, and humans; however, they may also be pollutants if they occur at high concentrations in soil. Therefore, knowledge of Cu and Zn cycling in soils is required both for guaranteeing proper nutrition and to control possible risks arising from pollution.rnThe overall objective of my study was to test if Cu and Zn stable isotope ratios can be used to investigate into the biogeochemistry, source and transport of these metals in soils. The use of stable isotope ratios might be especially suitable to trace long-term processes occurring during soil genesis and transport of pollutants through the soil. In detail, I aimed to answer the questions, whether (1) Cu stable isotopes are fractionated during complexation with humic acid, (2) 65Cu values can be a tracer for soil genetic processes in redoximorphic soils (3) 65Cu values can help to understand soil genetic processes under oxic weathering conditions, and (4) 65Cu and 66Zn values can act as tracers of sources and transport of Cu and Zn in polluted soils.rnTo answer these questions, I ran adsorption experiments at different pH values in the laboratory and modelled Cu adsorption to humic acid. Furthermore, eight soils were sampled representing different redox and weathering regimes of which two were influenced by stagnic water, two by groundwater, two by oxic weathering (Cambisols), and two by podzolation. In all horizons of these soils, I determined selected basic soil properties, partitioned Cu into seven operationally defined fractions and determined Cu concentrations and Cu isotope ratios (65Cu values). Finally, three additional soils were sampled along a deposition gradient at different distances to a Cu smelter in Slovakia and analyzed together with bedrock and waste material from the smelter for selected basic soil properties, Cu and Zn concentrations and 65Cu and 66Zn values.rnMy results demonstrated that (1) Copper was fractionated during adsorption on humic acid resulting in an isotope fractionation between the immobilized humic acid and the solution (65CuIHA-solution) of 0.26 ± 0.11‰ (2SD) and that the extent of fractionation was independent of pH and involved functional groups of the humic acid. (2) Soil genesis and plant cycling causes measurable Cu isotope fractionation in hydromorphic soils. The results suggested that an increasing number of redox cycles depleted 63Cu with increasing depth resulting in heavier 65Cu values. (3) Organic horizons usually had isotopically lighter Cu than mineral soils presumably because of the preferred uptake and recycling of 63Cu by plants. (4) In a strongly developed Podzol, eluviation zones had lighter and illuviation zones heavier 65Cu values because of the higher stability of organo-65Cu complexes compared to organo-63Cu complexes. In the Cambisols and a little developed Podzol, oxic weathering caused increasingly lighter 65Cu values with increasing depth, resulting in the opposite depth trend as in redoximorphic soils, because of the preferential vertical transport of 63Cu. (5) The 66Zn values were fractionated during the smelting process and isotopically light Zn was emitted allowing source identification of Zn pollution while 65Cu values were unaffected by the smelting and Cu emissions isotopically indistinguishable from soil. The 65Cu values in polluted soils became lighter down to a depth of 0.4 m indicating isotope fractionation during transport and a transport depth of 0.4 m in 60 years. 66Zn values had an opposite depth trend becoming heavier with depth because of fractionation by plant cycling, speciation changes, and mixing of native and smelter-derived Zn. rnCopper showed measurable isotope fractionation of approximately 1‰ in unpolluted soils, allowing to draw conclusions on plant cycling, transport, and redox processes occurring during soil genesis and 65Cu and 66Zn values in contaminated soils allow for conclusions on sources (in my study only possible for Zn), biogeochemical behavior, and depth of dislocation of Cu and Zn pollution in soil. I conclude that stable Cu and Zn isotope ratios are a suitable novel tool to trace long-term processes in soils which are difficult to assess otherwise.rn

Ammoniacal Sulphate Leach of Ananconda Zinc Calcine Recovery of the Zinc by Electrolysis.

Zinc is produced from ores by two general methods, distillation and electrolysis. The general principles involved in the electrolytic zinc process of today were known as far back as 1880. Difficulties encountered in purifying the solution for electrolysis and lack of suitable mechanical apparatus were the main reasons that such a long time elapsed before the process was used to produce zinc in commercial quantities.