Mostafa Benzaazoua

Chemical factors that influence the performance of mine sulphidic paste backfill

Sulphide-rich tailings from four Canadian mines were sampled (Mines A1, A2, B and C) to prepare several different paste backfill mixtures. The sulphur grade within these tailings samples range from 5 to 32 wt.%. The binders used were Portland-cement-based binders, fly-ash-based binders and slag-based binders with proportions ranging from 3 to 6 wt.%. The study was carried out in two stages. Stage I allowed us to understand the effects of binder type, binder proportion and tailings properties on compressive strength development of paste backfill during the course of curing time. It was pointed out that for high sulphide tailings, neither the slag-based binders nor the fly-ashbased binders were effective, whereas the sulphate-resistant-based binder (mix of Type I [TI] and Type V [TV] Portland cements) gave good long-term strength. However, the slag-based binders gave the best strength for low and medium sulphide-bearing tailings for which the Portland- and the fly-ash-based mixtures have a relatively low strength. Stage II allowed us to study the early stage strength acquisition of the various mixtures. It was found that the chemical composition of the mixing water plays a role on the mechanical behavior of certain cemented backfills. D 2002 Elsevier Science Ltd. All rights reserved.

Cementitious backfill with high sulfur content Physical, chemical, and mineralogical characterization

Abstract Use of cemented backfill in underground mining is common practice. The major economical benefits include increased recovery of ore and a reduction in the volume of waste requiring surface disposal. This paper presents new studies into the behavior of cemented backfill, namely, the chemical and mineralogical changes (weathering) with time that affect the mechanical strength of the fill. The weathering mechanism typically consists of sulfate attack. This process can occur rapidly during curing and depends on the binding agents used. The reaction involves dissolution of hydrated calcium phases followed by formation of expansive phases resulting in the degradation of the backfill’s mechanical properties. The use of fly ash, which is resistant to sulfate attack, generally reduces any strength deterioration. These phenomena are illustrated with a case study that demonstrates the influence of these alterations on the long-term mechanical properties of a cemented paste backfill sampled in situ.

Environmental desulphurization of four Canadian mine tailings using froth flotation

Abstract Environmental desulphurization is an attractive alternative for management of acid generating tailings. This process placed at the end of the primary process treatment circuit will reduce a large amount of the problematic tailings by concentrating the sulphide fraction. To produce desulphurized tailings, non-selective froth flotation is the most adapted method. The desulphurization level is fixed by the sulphide content of the tailings and their neutralization potential (NP). The final residue should have enough NP to safely compensate for its acidity potential (AP). In this paper, the authors present the results of a battery of tests conducted in Denver cells to study the sulphide flotation kinetics of four different mine tailings samples which contain 2.9 S%, 3.4 S%, 16.2 S% and 24.2 S%, respectively. Tailings P, M, and G are cyanide free and can be floated at pH values of less than 10 by using amyl xanthate as the collector agent. However, tailings D, which come from a gold cyanidation process, did not provide good sulphide recovery because of pyrite depression (even after cyanide elimination followed by a sulphide surface activation and a pH decrease). To successfully overcome this problem, amine acetate was used. This collector allows easy flotation without a pretreatment stage. Dosage of the two type of collector were optimized for the tailings studied. The results of all kinetic tests and collector dosage optimization were combined to establish a model which will estimate the cost of desulphurization. A preliminary analysis shows that the expense of the implementation of this desulphurization technology is comparable to other rehabilitation methods.

Physico-chemical properties of tailing slurries during environmental desulphurization by froth flotation

Abstract Environmental desulphurization has been established as an alternative solution to control acid mine drainage due to the reactivity of sulphide tailings when exposed to open air conditions. In fact, this process placed at the end of the primary treatment circuit greatly reduces the amount of problem tailings by concentrating the sulphide fraction. An acceptable target for sulphide content can be estimated from the acidity potential (AP), neutralization potential (NP) and the net neutralization potential (NNP) of the mill tailings. To produce desulphurized tailings, non-selective froth flotation is the most common method used in previous work. In this paper, the authors have focused the physicochemical properties of the pulp as the main parameters affecting the non-selective sulphide flotation. The pyrite depression due to lime addition during the former process represents the main problem. Several laboratory tests were conducted using a Denver cell to choose the best and most economical collector. Other tests were done to select the best frothing agent. The pH and redox potentials were investigated as parameters of great importance in flotation performance. For studying the sulphide flotation kinetics, two mine tailings are chosen which are characterized by a weak neutralization potential (under 37 kg CaCO3/t). Tailings S and L are cyanide free and contain respectively 5.27 and 10 wt.% sulphur. Collector dosage was optimized for these tailings as well as the flotation time and the results show that tailings L needed more collector than tailings S. Desulphurization costs were estimated to be CND

Prediction of Acid Mine Drainage: Importance of Mineralogy and the Test Protocols for Static and Kinetic Tests

0.35 per ton (dry tailings), which is very comparable and competitive to existing method for tailings management.

Arsenic stability in arsenopyrite-rich cemented paste backfills: A leaching test-based assessment

AbstractStatic tests, which compare the acid-generating potential and acid-neutralizing potential for a given mine waste (tailings or waste rocks), are characterized by a wide uncertainty zone in which it is impossible to accurately predict the acid-generating potential (AGP). Then, to better assess long-term AGP, kinetic tests are usually performed to provide more information about the reaction rates of the acid-generating and acid-neutralizing minerals. The present work compares the classic Sobek static test with three mineralogical static tests to assess the importance of sample mineralogy in acid mine drainage (AMD) prediction. We also investigated how experimental procedures related to static tests can influence prediction results. We used three synthetic tailings samples made by mixing well-characterized pure minerals in calibrated proportions. Although basically different in their principles and procedures, the modified Sobek and mineralogical static tests gave similar results. These AGP predictions were then validated by the use of a kinetic test. The kinetic test protocol was also modified in this study and the results obtained correlated well with the static test results, in contrast to the standard kinetic test protocol. The present work highlights the limitations of static and kinetic test procedures, and provides recommendations for a better use of these tests for more reliable AMD prediction. ZusammenfassungStatische Versuche, welche das säurebildende und -neutralisierende Potential von Bergbauabfällen bestimmen, weisen z. T. so große Unsicherheitsbereiche auf, dass das exakte säurebildende Potential (acid-generation potential, AGP) sehr schwer ermittelbar ist. Um das langzeitlich wirksame AGP zu bestimmen, werden häufig kinetische Test durchgeführt, um so die Reaktionsraten der säurebildenden und neutralisierenden Minerale zu ermitteln. In dieser Arbeit wird der klassische statische Versuch nach Sobek mit drei weiteren statischen Versuch verglichen, um die Bedeutung der mineralogischen Zusammensetzung der Proben bei der Vorhersage der Bildung von sauren Grubenabwässern zu untersuchen. Gleichzeitig wird betrachtet, wie sich die Versuchsbedingungen auf die Resultate auswirken. Hierzu werden drei künstliche hergestellte Mischproben verwendet, welche aus gut charakterisierten reinen Mineralen bestehen. Obwohl sich sämtliche Testvarianten hinsichtlich ihrer Grundlagen und Versuchsverläufe unterscheiden, führen sie zu vergleichbaren Ergebnissen. Die auf dieser Grundlage ermittelten AGP-Prognoseergebnisse wurden im Anschluss mit Hilfe eines kinetischen Versuchs validiert. Im Gegensatz zu standartgemäßen Versuchsverlauf wurde der kinetische Test verändert, was jedoch die Vergleichbarkeit mit den statischen Versuchen erhöht. In der vorliegenden Arbeit werden die Grenzen von statischen und kinetischen Versuchsanwendungen aufgezeigt und Hinweise zur Verbesserung der Versuche abgeleitet. Dies führt zu vertrauenswürdigeren Ergebnissen bei der Vorhersage der Bildung von sauren Grubenabwässern.ResúmenLos ensayos estáticos que compararan la capacidad de generación de ácido y la capacidad de neutralizarlo para cierto residuo minero (colas o rocas residuales) están caracterizados por una amplia zona de incertidumbre en la cual es imposible predecir adecuadamente la capacidad de generación de ácido (AGP). Luego, para un mejor relevamiento del AGP a largo plazo, los ensayos cinéticos se realizan usualmente para dar más información sobre las velocidades de las reacciones de generación y neutralización de la acidez que presentan los minerales. Este trabajo compara el ensayo estático clásico de Sobek con tres ensayos estáticos mineralógicos para relevar la importancia de la mineralogía de la muestra en la predicción de AMD. También investigamos cómo los procedimientos experimentales de los ensayos estáticos pueden influir en la predicción de los resultados. Usamos 3 muestras de colas sintéticas preparadas mezclando en proporciones definidas minerales puros bien caracterizados. Aunque difieren en sus principios y procedimientos, los ensayos estáticos mineralógicos y los estudios modificados de Sobek dan resultados similares. Estas predicciones AGP fueron luego validadas utilizando un ensayo cinético. El protocolo del ensayo cinético también fue modificado y los resultados obtenidos correlacionaron bien con los resultados del ensayo estático, en contraste con el protocolo estándar del ensayo cinético. Este trabajo clarifica las limitaciones de los procedimientos de los ensayos estáticos y cinéticos y aporta recomendaciones para un mejor uso de estos ensayos para una más exacta predicción del AMD.摘要静态试验用以预测某给定废矿石(尾矿或矸石)的产酸和酸中和潜力,试验方法具有不确定性,难以准确预测废矿石的产酸潜力(AGP)。动力学试验能够为更好地评价废矿石长期产酸潜力提供更多的产酸和酸中和反应速率信息。本文对比了经典索贝克静态试验(classic Sobek static test)和3种矿物学静态试验(mineralogical static tests)结果,以评价在酸性矿井水预测中样本矿物性质的影响。同时,研究了静态试验过程如何影响产酸预测结果。3种人工合成尾矿由纯矿物按标准比例混合而成。虽然改进的索贝克(modified Sobek)和矿物学静态试验(mineralogical static tests)原理和步骤不同,但它们的试验结果相似。动态试验验证了产酸潜力(AGP)预测的可靠性。本研究中的动态试验也为改进试验,动态试验结果与静态试验结果具有很好的一致性。文章突出了静态和动态试验方法的局限性,提出了合理利用这此试验方法进行酸性矿井水预测的建议。.

Oxygen diffusion and consumption in low-sulphide tailings covers

Arsenic (As) is a toxicant in tailings from sulphur deposits. It represents an environmental risk because of its high solubility. Tailings can be mixed with water (typically 25%) and a low proportion of hydraulic binder (3-7%) to produce a cemented paste backfill (CPB), stored in underground mine openings. CPB is a tailings storage technique, but it could also provide environmental advantages by stabilization of polluting elements such as As. Tailings from Casa Berardi mine (QC, Canada) contain As (3800 ppm), mainly in arsenopyrite form. For this study, three different CPBs were synthesized in laboratory using Casa Berardi tailings and three different binders. These pastes were submitted to various leaching tests after 28 days of curing. The results indicate that As is released at higher concentration for a fly ash-based CPB than for slag- and Portland cement-based CPB. However, at lower pH, As is better stabilized in fly ash-based samples. These differences can be explained by a variation of solubility of As-compounds in each CPB. Several mechanisms of As release occur, as diffusion and/or dissolution/precipitation. The accelerated weathering test results show that sulphide reactivity is buffered by the neutralizing minerals contained in CPB, and influence the As release behaviour by decreasing the oxidation of As-bearing sulphides.

Assessment of arsenic immobilization in synthetically prepared cemented paste backfill specimens

Acid-generating tailings can be reclaimed using oxygen barrier covers in humid climates, such as in Quebec. A single-layer low-sulphide tailings cover is an attractive alternative to traditional water covers to maximize the impoundment’s storage capacity. Low-sulphide tailings can serve as a moisture-retaining material to limit oxygen diffusion, and their residual sulphides can consume the diffusive oxygen that still gets through the cover. A laboratory experiment using instrumented columns was initiated to confirm the efficiency of a low-sulphide tailings monolayer cover placed over acid-generating tailings to reduce the oxygen flux reaching the reactive tailings. Oxygen concentration profiles were measured over the thickness of the cover and oxygen fluxes were calculated to evaluate the effect of three parameters on these fluxes: water table level, cover sulphide content, and cover thickness. Oxygen fluxes at the bottom of the low-sulphide tailings cover layer, calculated using oxygen gradient and estim...

Mineralogical distribution of some minor and trace elements during a laboratory flotation processing of Neves-Corvo ore (Portugal)

Mine tailings coming from the exploitation of sulphide and/or gold deposits can contain significant amounts of arsenic (As), highly soluble in conditions of weathering. Open mine voids backfilling techniques are now widely practiced by modern mining companies to manage the tailings. The most common one is called cemented paste backfill (CPB), and consists of tailings mixed with low amounts of hydraulic binders (3-5%) and a high proportion of water (typically 25%). The CPB is transported through a pipe network, to be placed in the mine openings. CPB provides storage benefits and underground support during mining operations. Moreover, this technique could also enhance contaminant stabilization, by fixing the contaminants in the binder matrix. CPB composites artificially spiked with As were synthesized in laboratory, using two types of hydraulic binders: a Portland cement, and a mix of fly ash and Portland cement. After curing duration of 66 days, the CPB samples were subjected to several leaching tests in various experimental conditions in order to better understand and then predict the As geochemical behaviour within CPBs. The assessment of the As release indicates that this element is better stabilized in Portland cement-based matrices rather than fly ash-based matrices. The As mobility differs in these two matrices, mainly because of the different As-bearing minerals formed during hydration processes. However, the total As depletion does not exceed 5% at the end of the most aggressive leaching test, indicating that As is well immobilized in the two types of CPB.

Assessment of the Modified CUAPS Apparatus to Estimate In Situ Properties of Cemented Paste Backfill

Abstract Neves-Corvo mine (SOMINCOR, Portugal) is one of the most important underground mines now operating in Europe. It treats a heterogeneous massive sulphide deposit, which is mainly copper and/or tin rich. The extracted ore is processed to obtain two types of concentrates (Cu and Tin) whose purity is affected by some minor (As and Sb) and trace (Hg, Se, Cd) elements. In addition to the concentrate sales, silver is also commercialized as a bonus product. The present work intends to identify the mineral bearer of some of these additional detrimental or bonus elements, and to develop a mineralogical model for predicting mineral processing production profits. Many laboratory-scale tests were conducted to study the behavior of minerals: the different steps and conditions of these tests allow good reproduction of the industrial flotation process of the Neves-Corvo mine. The statistical analyses of the elemental distributions give interesting results and provide the ingredients from which we can produce a preliminary predicting tool. Thus, fahlores-minerals (tetrahedrite and tennantite), which are considered to be veritable toxic trash minerals, can be easily localized during the process. This will allow their separation by modifying the flow sheet to improve the concentrate quality.