Evaluating waste rock mineralogy and microtexture during kinetic testing for improved acid rock drainage prediction

This study integrates detailed mineralogical and microtextural analyses of waste rock with the results of standard kinetic test procedures to identify the mineralogical changes that influence leachate chemistry over time. The integration of mineralogy and texture provides the opportunity for improved mine waste management strategies and acid rock drainage (ARD) prediction.Waste rock material from an abandoned gold mine in northern Queensland, Australia, was subjected to column leach kinetic testing over a 30 week period. The column feed comprised of a range of waste rock lithologies (porphyritic rhyolite, massive arsenopyrite, massive pyrite ± galena, and semi-massive polysulphide). In total, 12 individual columns were established to represent six lithologies prepared to two different size fractions (−10 mm and −4 mm). The mineralogy and microtextural characteristics of the column feed material was defined using quantitative X-ray diffractometry (QXRD), scanning electron microscopy and laser ablation (LA-ICPMS) at the start of kinetic tests, and at 5 week intervals during the length of the tests. These data were directly correlated with leachate chemistry (i.e., pH, SO₄ and select elements).Results of this study indicated that sulphide oxidation was strongly influenced by the morphology of sulphide minerals, their trace element contents, the presence of mineral micro-inclusions and galvanic interactions with other sulphide minerals. Waste rock with abundant arsenopyrite was consistently the most acid forming, and oxidised to scorodite (enriched in Zn, Pb and Cu). Pyrite was commonly As-rich as indicated by LA-ICPMS mapping. QXRD results indicated that the abundance of rhomboclase, jarosite, alunite and hydrous ferric oxides increased over time. Galena weathered rapidly to porous anglesite, particularly when in direct physical contact with pyrite. Sphalerite contents decreased consistently over the 30 weeks implying its oxidation, however few reaction products were directly observed. By week 30, the −4 mm fraction material generated lower pH leachate, higher mass release of elements and sulphate for the majority of samples. This indicates that the particle size used in kinetic tests can exert a significant control on leachate chemistry, especially in the absence of abundant neutralising minerals. This contribution demonstrates the value of integrating mineralogy and microtextural analyses during kinetic testwork to improve the interpretation of sulphide oxidation for better prediction of ARD.     

The process mineralogy of mine wastes

The discipline of process mineralogy developed through the recognition that metallurgical flowsheets could be optimised by thorough characterisation of the precursor ore mineralogy, mineral associations, grain size and textures. In a procedure analogous to process mineralogy it is shown here that effective characterisation of mine wastes for Acid Rock Drainage and Metal(loid) Leaching (ARDML) potential must follow a similar set of robust practices which include: (i) representative sampling; (ii) static/screening level geochemical tests and qualitative mineralogical assessment; (iii) longer-term kinetic geochemical tests and quantitative mineralogical assessment; and (iv) quantitative numerical modelling to assess source term chemistry associated with the mine facilities and thereby determine potential impacts to receptors. This process is dependent on a sufficiently robust drill core database and a detailed mine plan through which an assessment of mine wastes is possible. Such detailed characterisation may be limited by insufficient budgets, however omission of a thorough mineralogical investigation may lead to a lack of understanding of the primary geochemical controls on mine waste behaviour. In turn, this can lead to over- or under-engineering of mine facilities, which can have financial and/or environmental implications. Several case studies are presented to illustrate how mineralogy can be applied to solve problems in ARDML prediction and mitigation, specifically within waste rock assessment.     

The Global Acid Rock Drainage Guide (GARD Guide)

The International Network for Acid Prevention (INAP) has consolidated relevant information and produced a global acid rock drainage (ARD) guide (GARD Guide) that summarizes the best technical and management practices for industry and stakeholder use. The Guide provides a structured system to identify proven techniques for characterization, prediction, monitoring, treatment, prevention, and management of ARD. It will help industry to provide high levels of environmental protection, support government efforts in assessing and regulating mine reclamation, and enable the public to gain a higher degree of understanding of acid prevention plans and practices. This paper describes the organization and content of the internet-based GARD Guide. ARD management strategies are outlined to show GARD Guide principles in practice. Finally, the path forward for the GARD Guide is presented.     

Refinement of the isomorphic substitutions in goethite and hematite by the Rietveld method,and relevance to bauxite characterisation and processing

Although bauxites usually have a quite simple mineralogy – gibbsite (+boehmite), quartz, kaolinite, hematite, goethite, anatase (+rutile) and minor or less common phases, fine particle size, low crystallinity and variable compositions of the iron minerals might render phase quantification difficult, as well as impairing bauxite processing. A reliable and complete characterisation is therefore necessary in order to predict processing performance and ensure compliance to plant specifications.X-ray diffraction is the most important single tool for bauxite characterisation, and the constrained refinement of the Al-for-Fe substitution in goethite during one-step phase quantification by fundamental parameters Rietveld method has been successfully used. The same method was developed to analyse the coupled Al-for-Fe and OH⁻-for-O²⁻ substitutions in hematite. The method was tested against Mössbauer spectroscopy iron distribution on bauxite samples with a large compositional range, and on bauxite Certified Reference Materials from the main Brazilian mines, with improved results and widened range of conclusions that can be drawn related to bauxite processing.     

Characterisation of non-sulphide zinc deposits using QEMSCAN®

Non-sulphide zinc deposits are important potential resources of zinc and other metals, which require accurate characterisation of the mineralogy, texture and grade for successful processing. The mineralogy of these deposits has traditionally been examined using optical microscopy, cathodoluminescence, XRD, SEM and EPMA. This study develops QEMSCAN® technology to rapidly acquire spatially resolved mineralogical data from non-sulphide zinc ores from Accha (Peru) and Skorpion (Namibia). The resulting modal and textural data provides significant additional information on the distribution of the ore minerals including detail on the trace minerals, grain size distributions, and mineral associations. The data were verified by XRD to assess clays and compositionally similar mineral polymorphs and EPMA to accurately establish mineral compositions. The detailed mineralogical knowledge from this study improves the lithotyping of the deposits and will benefit the ore processing strategies for these complex deposit types. The particular processing implications include assessments of the acid consumption, the abundance and distribution of penalty elements, and potentially low zinc recoveries relating to iron oxyhydroxides and sauconite.     

青海某低品位铁矿的工艺矿物学研究

对青海某沉积变质型低品位铁矿进行了工艺矿物学研究,研究结果表明,矿石铁低、硅高、有害杂质磷、硫低;铁矿物类型复杂且粒度微细,以磁铁矿为主,次为菱铁矿、赤铁矿,与含硅脉石矿物嵌布关系复杂,特别是与微细粒绿泥石嵌布关系密切。依据工艺矿物学研究成果,重点分析了矿石难选的最关键原因,为低品位沉积变质型难选铁矿开发利用提供矿物学参考依据。     

A critical review of acid rock drainage prediction methods and practices

Failure to accurately predict acid rock drainage (ARD) leads to long-term impacts on ecosystems and human health, in addition to substantial financial consequences and reputational damage to operators. Currently, a range of chemical static and kinetic tests are used to evaluate the acid producing nature of materials, from which risk assessments are prepared and waste classification schemes designed. However, these well-established tests and practices have inherent limitations, for example: (i) best-practice sampling is not pursued; (ii) risk assessments rely on limited static and kinetic test data, thus compromising the accuracy of resulting ARD block models; (iii) static tests are completed off-site and do not reflect actual field measurements; (iv) kinetic test data do not become available until later stages of mine development; (v) waste classification schemes generally categorise materials as only three types (i.e., PAF, NAF and UC) with other drainage forms (e.g., neutral metalliferous or saline) not considered; and (vi) conventional testing fails to consider that reactivity of waste is controlled by parameters other than chemistry (e.g., microbiology, type and occurrence of minerals, texture and hardness). Thus, accurate prediction is challenging because of the multifaceted processes leading to ARD. Hence, risk assessments need to consider mineralogical, textural and geometallurgical rock properties in addition to predictive geochemical test data. Instead, a new architecture of integrative, staged ARD testing should be pursued. Better ARD prediction must start with improving the definition of geoenvironmental models and waste units. Then, a range of low-cost and rapid tests for the screening of samples should be conducted on site prior to the performance of established tests and advanced analyses using state-of-the-art laboratories. Such an approach to ARD prediction would support more accurate and cost-effective waste management during operation, and ultimately less costly mine closure outcomes.     

新疆滴水铜矿石工艺矿物学研究

新疆滴水铜矿开发利用前,由于缺乏深入的工艺矿物学研究,因而该资源的综合利用水平不高。为改善该状况,对有代表性矿石进行了较系统的工艺矿物学研究。结果表明：①矿石中铜矿物种类繁多,以氧化铜矿物为主,约占总铜矿物的83%以上,硫化铜及自然铜不足总铜的17%。主要含铜矿物有孔雀石、赤铜矿、硅孔雀石、黑铜矿、蓝铜矿、铜蓝、辉铜矿、斑铜矿、黄铜矿等。②矿石中的脉石矿物主要有石英（燧石）、斜长石、微斜长石、条纹长石、黑云母,方解石,蚀变矿物主要有绿泥石、绿帘石等。③矿石的主要结构形式有砂状结构、泥状结构、棱角状结构、交代溶蚀结构、束状结构和皮壳状结构,主要构造形式有层状构造、浸染状构造、条带状构造、块状构造、网纹状构造等。④各种铜矿物嵌布特征差异较大,且嵌布粒度粗细极不均匀,最小粒仅为0.001 mm左右,最大粒一般为1 mm左右,有的甚至达15 mm。系统的工艺矿物学分析为确定科学合理的选矿工艺流程及工艺参数提供了重要的理论依据。     

自动矿物分析系统的统计误差分析

通过简化假设,提出了工艺矿物学中矿物体积百分含量p、统计量n与相对误差E的数学模型。对给定目标矿物的体积百分含量、统计颗粒数和置信度,可以估算出目标矿物的测量误差。采用四种矿物调配成已知含量的样品,用于验证自动矿物分析系统的测量精度。验证试验表明,当统计量越大时,不同含量的矿物的测量值均向理论值收缩,反之统计量变少时其测量值越偏离理论值,造成统计误差增大。通过对统计量的选择,可以实现对不同品位矿石的工艺矿物学参数的准确测量。     

Calcium Carbonate in Waste Flooring for Neutralization of Acid Rock Drainage

Mine Water and the Environment - Acid rock drainage (ARD) was successfully neutralized in this study using carpet tiles. Most polyolefin-based carpet tiles contain over 65% of finely ground calcium...     

辽宁某铜铅锌多金属硫化矿工艺矿物学研究

对辽宁某铜铅锌多金属硫化矿矿石进行了工艺矿物学研究,重点查明矿石的结构、构造,矿物组 成,铜、铅、锌的赋存形式及主要矿物的嵌布特性。研究结果表明,矿石中的金属硫化物间及硫 化物与脉石矿物间嵌布关系密切而复杂,存在铅铜及锌铜包含关系,将对铜铅锌的分选产生不利 影响。研究结果可为该多金属硫化矿浮选原则流程的选择提供参考依据。     

矿物自动定量分析系统在低品位微细粒钼矿工艺矿物学研究中的应用

钼是一种重要的战略矿产资源,素有"能源金属"、"战争金属"之称.利用中国首套具有自主知识产权的矿物自动定量分析系统——工艺矿物学自动分析仪(BPMA),结合化学分析、X射线衍射(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)和能谱仪(EDS)等分析手段,对陕西某低品位微细粒钼矿的工艺矿物学特征进行了自动、快速、...     

云南某含钴铜矿工艺矿物学研究

矿石工艺矿物学研究能为矿石加工方案选择提供理论支撑,为更科学合理地利用云南某含钴铜矿,对其代表性矿样进行了工艺矿物学研究.经查明,矿石中铜含量为1.82％,主要以独立矿物的形式存在于砷黝铜矿(占97.11％)、黄铜矿(占2.89％)中;钴含量为0.033％,主要以独立矿物的形式赋存于辉砷钴矿中(占51.52％),以类质...     

Smelter feed quality control

Final concentrates and furnace feeds from Anglo American Platinum are routinely monitored for quality. Merensky Reef, UG-2, and Platreef concentrates are sampled at the concentrators, as well as blended feed at the smelters, and the composition and mineralogy of these samples are determined at Anglo American Research.This information allows the smelting characteristics of the concentrates to be predicted. Parameters such as the matte fall, spinel formation, and smelting energy requirement can be calculated by modelling.The concentrates are characterised by chemical analyses for base metals, precious elements and trace elements. Various QEMSCAN techniques are used to determine the mineralogy of the samples and the abundance of gangue minerals and base metal sulphides (BMS), as well as the mineral association, are reported.     

云南二郎铜矿石工艺矿物学研究

为给云南二郎铜矿资源合理开发利用提供依据,对矿石进行了工艺矿物学研究。结果表明:该矿石原岩由岩屑角砾岩、岩屑杂砂岩、变质岩屑石英砂岩等组成,主要结构为填隙结构、他形粒状结构矿石;主要构造为稠密浸染状构造、稀疏—星散浸染状构造。矿石中主要目的元素铜品位为1.72%,矿石中的铜主要为游离氧化铜,占总铜的89.89%,结合氧化铜占总铜的5.85%;铜矿物主要是孔雀石(蓝铜矿)、砷钙铜矿、含铜褐铁矿、假孔雀石;脉石矿物主要为石英、白云母、方解石。矿石中的孔雀石(蓝铜矿)多数呈半自形—他形粒状嵌布于脉石矿物中,+13.5μm粒级分布率为70.09%;砷钙铜矿集中分布在27~3.4μm粒级,累计分布率达88.85%;含铜褐铁矿的嵌布特征较复杂,部分以粗粒单体形式存在,粒度主要集中分布在+38μm粒级,累计分布率达71.61%。根据该矿石的工艺矿物学特征,宜采用酸浸工艺回收该铜资源。     

Environmental management of acid water problems in mining areas

Acid Mine Drainage (AMD) originates from the oxidation and leaching of sulphide minerals present in coal and metalliferrous ore bodies and gives rise to several environmental degradation problems. An investigation has been carried out to combat the acidic water problems. Results of this investigation indicate that application of anionic surfactant (sodium lauryl sulphate) and food preservatives (sodium benzoate and potassium sorbate) effectively abate the acid formation at low concentration levels (15–40 ppm) as tested in laboratory as well as at pilot-scale levels. Acidity, sulphate and iron concentrations are found to reduce by over 70 percent and remained low for more than three months after treatment. Thus this investigation demonstrates the management of these problems in an environmentally safe manner by controlling acid formation at its source.     

Release of Aluminum from Clays in an Acid Rock Drainage Environment

Aluminum concentrations in low pH acid rock drainage (ARD) commonly exceed the freshwater aquatic toxicity threshold. An Al-containing ARD released from pyritic sandstone and shale fill along US. Interstate 80 in Center County, Pennsylvania has adversely impacted a former fishing stream. This ARD consistently contains low concentrations (<2 mg/L) of Fe and high concentrations (≈48 mg/L) of Al. Batch experiments conducted with kaolinite and H/Al-bentonite clays and clay soils collected from the Centre County, PA area suggests that synthetic brackish ARD enhances the release of Al from these clays, compared to synthetic acid (sulfuric) only and non-brackish ARD. This implies that highway deicing salts in road runoff could aggravate the leaching of Al from pyritic rocks used as fill or exposed in road cuts. Likewise, the use of ARD to enhance the production of natural gas from tight shales could result in the leaching of Al. Quantification of levels of Al released from field clays could be critical when considering remediation strategies.     

矿产资源综合利用中值得重视的几个问题

论述了矿产资源综合利用中值得重视的几个问题：正确理解矿物在自然界中的"分布"概念,矿物的物理性质和物理化学性质的全面研究,矿物中所含有价杂质元素的价值,新矿物的发现,处理新型矿物原料工艺流程的制定,对新大陆圈（包括海底矿物）矿物学研究和矿物作收藏品等。     

Environmental Aspects of a Major ARD Source at El Indio Au-Cu-As District,North-Central Chile

El Indio, an Au-Cu-As deposit with outstanding gold grades, was mined in the Andes of the Coquimbo region, Chile, between 1975 and 2002. Sediment and water sampling of the rivers in the 2000 s found exceptional As and metal levels in modern and old sediments. The studies also revealed that acid rock drainage (ARD) has been present in the district for nearly 10,000 years and the effect that the mining of the district had in terms of geochemical anomalies. The convergence of mineralogical, structural, and hydrologic conditions has generated a metal-rich ARD, a process followed by transference of metals to the fine sediments. In this context, the study also deals with the risk of metal and metalloid transfers from the sediments to the river waters as a consequence of eventual physical-chemical changes, due for example, to climatic-driven conditions. Water and sediment samplings were carried out to provide materials for selective extraction tests under acidic, acid-reducing, and acid-oxidizing conditions. The different behavior of metals and metalloids was revealed and highlighted the refractory character of As. Additionally, the study included the characterization of the sediment’s mineralogy, and allowed the detection of new geochemical anomalies of Cu, Zn, Co, and Y in the Incaguaz River, along with high dissolved Li concentrations in the Toro and Turbio rivers.

     

Development of a textural index for the prediction of acid rock drainage

The acid rock drainage index (ARDI) was developed to predict acid formation based on intact rock texture. Five textural parameters which have direct control on acid formation are evaluated. The ARDI forms part of the geochemistry-mineralogy-texture (GMT) approach to undertaking acid rock drainage (ARD) predictive tests. This staged-approach involves parallel use of geochemical, mineralogical and textural analyses. Sample screening is performed at stage-one, and a general classification given. Stage-two involves the use of routine geochemical tests in order to cross-check stage-one results, and also to quantify the acid forming/neutralising potential. Stage-three uses advanced geochemical tests and microanalytical tools to cross-check any ambiguous results from the previous stages, and for detailed characterisation of acid forming sulphide phases.Samples were obtained from two mine sites in Queensland, Australia, from which seventeen mesotextural groups were identified (A-Q). The ARDI identified mesotextural groups J (quartz-pyrite) and H (quartz-arsenopyrite-pyrite) as extremely acid forming. Routinely used geochemical classifications also identified these as the most acid forming groups. Four mesotextural groups (K-O) were classified as having acid neutralising capacity after full GMT classification. The remainder of mesotextural groups were classified as not acid forming. Mesotextural groups G (quartz-galena-sphalerite), H and J only require kinetic testing to resolve the lag-time to, and longevity of acid formation, and to measure the concentration of potentially deleterious elements released. The ARDI was not able to confidently discern between samples with the capacity to neutralise acid, and those which are not acid forming. Therefore, further refinement of the ARDI is required. However, in its current form the ARDI is suitable for mineral deposits with low-carbonate contents. This paper demonstrates its use as part of stage-one of the GMT approach at both operational and abandoned mine sites to screen and classify acid forming potential.