Investigation of the potential for mineral carbonation of PGM tailings in South Africa

Increasing atmospheric CO₂ concentration is currently of considerable concern in terms of global warming. A possible technology that can contribute to the reduction of CO₂ emissions is its sequestration by mineral carbonation. In this study, tailings from several different platinum mines in South Africa will be mineralogically characterised and their potential for mineral carbonation reviewed. Mg and Ca-rich minerals (plagioclase, olivine, orthopyroxene, clinopyroxene) present in the tailings are good candidates for mineral carbonation, which mimics natural weathering processes in which these minerals react with gaseous CO₂ to form Ca or Mg carbonates. Since the reaction is influenced by particle surface area, the ultra fine grained nature of the PGM tailings provides another reason for the promise of PGM tailings for mineral carbonation. A preliminary ranking of the tailings samples and their efficacy for mineral carbonation has been developed according to whether the samples showed harzburgtic (e.g. Northam Platinum mine), pyroxenetic (e.g. BRPM) or noritic mineral assemblages. This information and understanding will assist in identifying opportunities and guiding the development of engineered facilities for the sequestration of CO₂ by means of mineral carbonation.     

Magnesium chloride as a leaching and aragonite-promoting self-regenerative additive for the mineral carbonation of calcium-rich materials

Two approaches for the intensification of the mineral carbonation reaction are combined and studied in this work, namely: (i) the calcium leaching and aragonite promoting effects of magnesium chloride (MgCl₂), and (ii) the passivating layer abrasion effect of sonication. The alkaline materials subjected to leaching and carbonation tests included lime, wollastonite, steel slags, and air pollution control (APC) residue. Batch leaching tests were conducted with varying concentrations of additives to determine extraction efficiency, and with varying solids-to-liquid ratios to determine solubility limitations. Aqueous mineral carbonation tests, with and without the use of ultrasound, were conducted applying varying concentrations of magnesium chloride and varying durations to assess CO₂ uptake improvement and characterize the formed carbonate phases. The leaching of calcium from lime with the use of MgCl₂ was found to be atom-efficient (1 mol Ca extracted for every mole Mg added), but the extraction efficiency from slags and APC residue was limited to 26–35% due to mineralogical and microstructural constraints. The addition of MgCl₂ notably improved argon oxygen decarburization (AOD) slag carbonation extent under sonication, where higher additive dosage resulted in higher CO₂ uptake. Without ultrasound, however, carbonation extent was reduced with MgCl₂ addition. The benefit of MgCl₂ under sonication can be linked to the preferential formation of aragonite (85 wt% of formed carbonates), which precipitates on the slag particles in the form of acicular crystals with low packing density, thus becoming more susceptible to the surface erosion effect of sonication, as evidenced by the significantly reduced carbonated slag particle size.     

高能球磨对WC-10Co硬质合金组织性能影响

采用三维混料及高能球磨工艺制备WC-10Co混合粉,通过压制烧结工艺制备WC-10Co硬质合金,用SEM、EDS和XRD测试分析硬质合金组织结构。结果表明：与混合工艺制备粉末相比,球磨工艺制备的粉末产生细化、变形及均匀包裹,粉末分布更均匀;制备硬质合金的组织主要由WC、Co、η和γ相组成;球磨粉末在烧结过程中形成较均匀液相,可改善因三维混合粉末分布不均导致的W、C元素在Co中的过分溶解,抑制WC脱碳,并且较细的WC和Co颗粒使形核点显著增加,促使晶粒细化,洛氏硬度、抗弯强度增大。     

Valorization of steel slag by a combined carbonation and granulation treatment

This work reports the results of a combined accelerated carbonation and wet granulation treatment applied to Basic Oxygen Furnace (BOF) steel slag with the aim of producing secondary aggregates for civil engineering applications and of storing CO₂ in a solid and thermodynamically stable form. The tests were carried out in a laboratory scale granulation device equipped with a lid and CO₂ feeding system. In each test, humidified slag (liquid/solid ratio of 0.12 l/kg) was treated for reaction times varying between 30 and 120 min under either atmospheric air or 100% CO₂. Under both conditions, the particle size of the treatment product was observed to increase progressively with reaction time; specifically, the d₅₀ values obtained for the products of the combined granulation and carbonation treatment increased from 0.4 mm to 4 mm after 30 min and to 10 mm after 120 min. Significant CO₂ uptake values (between 120 and 144 g CO₂/kg) were measured even after short reaction times for granules with diameters below 10 mm and for the coarser particle size fractions after reaction times of 90 min. The density, mineralogical composition and leaching behavior of the obtained granules were also investigated, showing that the combined granulation–carbonation process may be a promising option for BOF slag valorization, particularly in terms of decreasing the Ca hydroxide content of the slag. Another interesting finding was that the leaching behavior of the product of the combined treatment appeared to be significantly modified with respect to that of the untreated slag only for coarse uncrushed granules, an indication that the carbonation reaction occurs mainly on the outer layer of the formed granules.     

纤维掺量对钢渣薄板碳化固结特性的影响研究

钢铁行业CO2排放量大,钢渣等冶金固废资源化利用困难。钢渣碳化材料安定性和耐久性良好,但抗拉强度低、易开裂,限制了其在建筑领域的应用。本文采用钢渣为碳化原料、聚丙烯纤维为增强材料、碳化养护为手段开发制备纤维增强钢渣碳化材料。以钢渣碳化材料抗压强度、抗折强度和碳酸化程度为判断依据,结合热重、压汞法等微观分析方法,研究聚丙烯纤维掺量对钢渣碳化材料力学性能、碳化固结性能的影响规律。研究发现聚丙烯纤维的加入会降低钢渣碳化材料的抗压强度,但适量的纤维掺入对于提高钢渣碳化材料抗折强度是有利的,随着纤维掺量的增加,钢渣碳化材料抗折强度呈现出先不变,后增加,再减小的变化趋势,在纤维掺量为7 kg/m3时达到最大值。此外,聚丙烯纤维的加入会促进钢渣的水化反应,降低钢渣的碳化反应,提高钢渣碳化材料的密度,降低钢渣碳化材料的孔隙率,但会提高碳化反应生成的碳酸钙的热稳定性。本文的研究结果对其它高钙镁含量材料制备碳化纤维薄板提供参考。     

Calcium leaching from waste steelmaking slag: Significance of leachate chemistry and effects on slag grain mineralogy

Accelerated carbonation of alkaline wastes such as steelmaking slag offers the potential to combine waste valorisation with climate change mitigation by utilising carbon dioxide (CO₂). One method of achieving this is through an indirect carbonation process to produce a marketable precipitated calcium carbonate (PCC), using ammonium salts to selectively extract calcium from steelmaking slag. Two unaddressed design parameters for a slag based plant differing from that of a traditional PCC plant are the effect of mineralogy on extraction efficiency when using a multicomponent, heterogeneous feed such as slag and the challenges raised by the resulting leachate chemistry. This paper presents petrographic textural observations on the effect of calcium leaching via ammonium chloride on individual grains of dicalcium silicate in three different widely unutilised steelmaking slags. These observations are then interpreted in conjunction with measured changes in solution leachate chemistry. The results indicate that although silica enriched regions form at the reaction front, the reaction continues into the core of the particle due to fracture propagation caused by volume reduction as calcium is extracted. Co-leaching of sulfur alongside calcium and the formation of precipitate in the leachate highlights potential engineering challenges when the process is scaled up due to fouling of process equipment. The main mineral phases in all untreated slags were found to be calcium silicates, predominantly dicalcium silicate (Ca₂SiO₄). This was followed by a complex mixture of calcium/magnesium-wustite (CaFeMnMg)O type phases and srebrodolskite (Ca₂Fe₂O₅(Ti, V)). Results indicate that calcium silicate is the more reactive component of BOS slag, while lime bound as (CaFeMnMg)O is most reactive in HMD and SS slags. Selectivity of the ammonium chloride solvent was high at 95–97% and efficiency of calcium extraction ranged between 25% and 39%.     

基于神经网络的数控铣削参数工艺效果预测

针对数控铣削加工工艺的复杂性,以DMC60H为平台,以壳体类铝合金零件加工工艺数据为对象,提出了基于神经网络的数控铣削参数工艺效果预测方案。预测结果表明,所建立的工艺效果预测模型能够比较精确地预测出给定加工参数下的加工时间、尺寸精度和表面粗糙度,实现了数控铣削参数的合理选取,充分发挥了机床效能,提高了产品质量和生产效率,为生产实践提供了理论依据。     

均相沉淀法制备碳酸锶粒子及其形貌控制研究

以八水氢氧化锶与尿素为原料采用均相沉淀法,通过添加控制剂合成不同形貌的碳酸锶粒子.结果表明:添加不同控制剂对粒子粒度和形貌具有一定的影响.通过电子显微镜和XRD表征表明,在没有添加控制剂时制备出了纺锤状和柱状的碳酸锶粒子,粒度分别为4～6um和2～3um,长径比分别约为6∶1和10∶1; 添加EDTA、三聚磷酸钠和硝酸铈等制备出了线状、棒状等碳酸锶粒子,粒子粒度明显减小.其晶体均属于正交晶系.     

DEM validation of media shape effects on the load behaviour and power in a dry pilot mill

Simulations were carried out in Metso’s DEM simulator so as to draw up an understanding of the effects the various ways of defining media shapes within the simulator have on the load behaviour and mill power draw. Wits University made available the load behaviour and mill power draw experimental results for the spherical balls, worn balls and cylpebs so as to validate the DEM simulations. The spherical media were defined by a regular spherical shape model and a multi-faceted polyhedron model. Worn balls were defined by super quadric models. A comparison was made between spherical media shapes, non-spherical single media shapes and a distribution of non-spherical media shapes and sizes in representing a load comprised of worn balls. The effect of increasing angularity of non-spherical media shapes on mill power was investigated. The cylpebs were modelled using a regular cylindrical shape model and the effects of friction on the power drawn were determined.     

球磨工艺对FeSiAl合金的制备和电磁性能的影响

以Fe,Si,Al为原料,采用高能球磨技术制备了FeSiAl合金粉末,研究了不同球料质量比,球磨时间对粉末的相结构,形貌和微波电磁性能的影响。结果表明： FeSiAl完成合金化的球料质量比为40:1,球磨时间为100h。随着球磨时间的增加,粉体的磁导率增加,而介电常数得到了降低,因而阻抗匹配更加优异。FeSiAl合金体积分数为35%的吸波材料,在厚度2mm时,在8.5GHz处,具有较低的反射率(-18.3dB)。     

The colouring effect of pyrrhotite and pyrite on micronised calcium carbonate slurries for the paper industry

Brightness (R457) is the main quality parameter in the production of ground calcium carbonate (GCC) slurries for the paper industry. In order to study how the presence of trace amounts of pyrrhotite (Fe_(1−x)S) and pyrite (FeS₂) affect the brightness of GCC slurries, experiments were performed in which a high quality calcite concentrate was spiked with these sulphides prior to micronisation and subsequent spectrophotometric measurements. The results show that even very small additions (<0.05 wt%) have a significant detrimental effect on the brightness of the product. Pyrrhotite reduces the brightness of the product more than pyrite, probably as an effect of differences in inherent optical reflectivity, specific surface area after micronisation and smearing. In addition, the experiment shows that when brightness is presented as a function of iron concentration, magnetite (Fe₃O₄) produces a different result compared to the sulphides. This indicates that a simple iron analysis is not sufficient to predict brightness of the GCC slurry when several iron-bearing minerals are present. The particle size distribution of the contaminant phase has proven to have a significant effect, as brightness is reduced when the contamination becomes more finely distributed.     

Effect of accelerated carbonation on the microstructure and physical properties of hybrid fiber-cement composites

Carbonation takes place in the fiber-cement composites through the diffusion of carbon dioxide (CO₂) through the unsaturated pores of the cement matrix, and through its reaction with the hydration products of the Portland cement (mainly calcium hydroxide and CSH phases). The use of this technology in the fiber-cement production consists of an interesting procedure to prematurely decrease the alkalinity of the cement matrix, which is potentially harmful to the cellulose fiber reinforcement. It is also an initiative to CO₂ sequestration and partial replacement of petroleum-based fibers. Therefore, the objective of the present work is to show the impact of accelerated carbonation on the microstructure and physical properties of fiber-cement composites reinforced with cellulose pulp and synthetic fibers. The effectiveness of the accelerated carbonation was confirmed by thermogravimetric (TG) analysis. Accelerated carbonation increased bulk density (BD) and decreased apparent porosity (AP). The SEM micrographs show that the calcium carbonate (CaCO₃) formed from the carbonation reaction is precipitated in the pore structure of the matrix. The interface between the cellulose fibers and the cement matrix in the carbonated composites was improved, decreasing the typical voids around the cellulose fibers that prejudice the fiber-cement performance at long term.     

数控铣床刀具半径补偿功能特征及分析应用

刀具半径补偿是数控机床中非常有用的功能之一 ,利用刀具半径补偿功能可以减化程序编制。同一加工程序可实现分层铣削、粗、精加工或用于提高加工精度。主要论述数控铣床刀具半径补偿功能特征及用途 ,通过对刀具半径补偿在编程、加工时出现的一系列问题进行分析研究 ,并提出了避免发生机床报警或过切现象的防范措施     

Wear performance and cost effectiveness––a criterion for the selection of grinding media for wet milling in mineral processing operations

Experiments to evaluate the milling performance, hence the relative cost effectiveness index of selected grinding media were conducted in a laboratory scale ball mill. The five types of grinding mill balls studied were eutectoid steel, low alloy steel, medium chromium cast iron, cast semi-steel and unalloyed white cast iron. The results obtained show that the heat-treated medium chromium cast iron ball possess a superior combination microstructure, wear resistance, and despite its high price per tonne, cost effectiveness.     

The influence of the density of a gas-solid fluidized bed on the dry dense medium separation of lump iron ore

A gas-solid fluidized bed was used for dry dense medium separation of lump iron ore particles based on their floating and sinking in the fluidized bed. The density of the bed was adjusted to different values using mixtures of zircon sand and iron powder as the fluidized media. Float-sink experiments using 30 mm diameter density adjusted spheres in the range of 2100-4500 kg/m³ in density increments of 100 kg/m³ were carried out to determine the partition curves, the density of the bed and the probable error (Ep). It was found that the density could be adjusted in the range of 2500-4200 kg/m³, when the bulk volume fraction of iron powder and the fluidizing air velocity were varied. The Ep values were less than or equal to 0.05, if suitable fluidizing air velocities were chosen. The density of the bed determined using the spheres floating-sinking corresponds to that measured using the height of the fluidized bed. The float-sink performance of lump iron ore particles in the size range of +25-31.5 mm agrees well with the spheres’ float-sink performance. The partition curves, separation density and the Ep values were determined for the lump iron ore particles. The Ep value for the ore particle separation was around 0.03. The theoretical Fe-grade recovery (washability) curve for the ore was determined for separation densities between 2500 and 4200 kg/m³ from the density distribution and Fe content of the lump iron ore particles. The actual Fe-grade and recovery were calculated from the partition curves of the ore particle separation and compared to the theoretical maximum obtainable Fe-grade and recovery.     

楔形铣刨刀具受力计算模型及其影响规律分析

为满足戈壁地表砂土的铣刨收集要求,通过对铣刨切削装置的工作原理、旋转方式和铣削运动参数的理论分析,建立了楔形铣刨刀具砂土切削的力学计算的数学模型。根据收集研究区域不同深度砂土的材料强度,利用该数学模型并运用计算机仿真,研究了楔形铣刨刀具的运动参数、几何参数与切削受力之间的关系,得出了给定条件下楔形铣刨刀具设计参数对砂土切削受力的影响规律,研究成果为楔形铣刨刀具结构及其收集工艺参数的优化设计奠定基础。     

年产5万t超细重钙生产线的设计实践

本文介绍了四川石棉巨丰粉体有限公司年产5万t超细重钙干法生产线的设备选型、研磨设备的改进及其系统生产工艺的优化。生产实践表明:有效减少了系统过研磨、提高了研磨效率和分级效率。     

西澳大利亚州矿产资源概况及矿产勘查投资建议

西澳大利亚州矿产资源丰富,政局稳定,法律建全,是国内地勘单位走出去投资矿产勘查的主要地区,但很多项目在实施过程中都碰到了一些问题,取得成功的项目非常少。本文对西澳大利亚州的成矿地质背景和主要的矿产种类进行了概况研究,并提出了矿产勘查投资存在的主要问题:项目信息收集不全、选区不在主要成矿带上、经济评价存在问题以及存在环境和土著权的问题。并针对这些问题提出了几点投资建议:在投资理念方面应按照商业文化理念来思考问题;投资运作方面可以通过期权转让和合作勘查的方式获取探矿权;投资决策方面主要按照西澳州投资决策的四个要素;在勘查方法方面,使用最真接、有效的方法进行快速评价。     

Effect of cuprous cyanide,dry and wet milling on the selective flotation of galena and sphalerite

Batch flotation tests of a lead–zinc sulphide composite ore from the Rosh Pinah Mine have been carried out at pH 8.5 in the presence of copper cyanide complexes. These copper cyanide complexes are often found in the recycled water that is used in the milling and the lead flotation circuits. Flotation results have shown that cuprous cyanide complexes can activate sphalerite. In addition, the activation and subsequent flotation of sphalerite was greater when the composite was dry milled as compared to wet milling. Surface analysis of copper(I)-activated sphalerite samples was studied by X-ray photoelectron spectroscopy (XPS). XPS results showed the presence of copper species on the surface of sphalerite after activation with cuprous cyanide complexes. The copper species could be removed from the surface of sphalerite after treatment with sodium cyanide. This explains, amongst others reasons, the high cyanide requirement at Rosh Pinah Mine for the efficient depression of sphalerite in the lead flotation circuit.     

超细粒级浸出渣与棒磨砂混合胶结充填强度试验研究

为解决凡口铅锌矿超细粒级浸出渣废弃的问题,探究灰砂比、浸出渣与棒磨砂的配比、料浆浓度对充填体强度的影响。设计正交试验并进行浸出渣与棒磨砂混合胶结充填试验,得出各因素对充填体强度影响的重要性顺序,确定出最佳充填配比参数。结果表明,各因素影响充填体强度的重要性顺序为料浆浓度灰砂比浸出渣与棒磨砂的配比;最佳充填配比参数为灰砂比1∶4、浸出渣与棒磨砂的配比1∶6、料浆浓度77%。对不同条件下充填体强度增长规律进行分析,得出充填体强度增长规律:增大灰砂比、料浆浓度可提高充填体强度;在一定范围内,充填体强度随浸出渣用量的增加而提高;细颗粒尾砂越多,充填体水化反应时间越长;充填体强度的增长过程分为增长早期、快速增长期和增长平稳期。