Seawater-softening process through formation of calcite ooids

Conventional water-softening processes usually involve the exchange of Na⁺ ions for Ca²⁺ and Mg²⁺ using commercial or synthesized ion exchangers. The differences in chemical compositions of the ooids can be attributed to the formation in different environments. In this paper, ooid grains form inside assembled semi-pilot softening unit through a continuous chemical process involving reaction between bicarbonate ions and added lime using natural seawater. Our sample of Mediterranean seawater has low Mg²⁺/Ca²⁺ ratio (1.98%) within the range chemically favorable for precipitation of low-Mg calcite ooids. Precipitation of calcite occurs around pure quartz sand grains which act as nucleation points (the bed required for sand vessel is 1.65 l). The shape of the sand grains controls the overall external morphology of the resulting ooids; they vary in size from 0.5 to 3.0 mm and have a high degree of polish due to surface abrasion caused by continuous agitation inside the softening system. Calcite ooid grains (1.53 kg) formed within the seawater-softening unit every 18 days have many of the ooid features formed in marine environments. Ooids grow to a significant size, at a rate of about 0.17 mm of one layer thickness per day inside the softening unit. The average weight percent of calcite precipitate is 35.48% after 18 days, at 10 °C, 60 l/min and pH 9.0. The pellets comprise mainly CaCO₃ and SiO₂ and some metal ions which may substitute for calcium ions in calcite are present only in trace amounts of the total composition.     

Formation and decomposition of C4F7 type calcium ferrites in superfluxed magnetite based pellets during oxidation and reduction

Abstract

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO)₄(Fe₂O₃)₇, whereas the one commonly reported in the literature is (CaO)(Fe₂O₃)₂. During reduction at 500–700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wüstite at 800°C, the calcium began dissolving in the wüstite, and at 900°C porous calciowüstite had formed in the entire sample, except for some remaining magnetite left in the pellet cores.     

Synthesis and characterization of hydrophobic calcium carbonate particles via a dodecanoic acid inducing process

A carbonation route for the synthesis of hydrophobic calcium carbonate was studied. In the process, dodecanoic acid was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and dodecanoic acid by bubbling CO₂/N₂ gas mixture. The operating parameters such as temperature and the concentration of the organic substrate were varied to study their influences on the active ratio and contact angle of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with scanning electron microscopy (SEM). The synthesized calcium carbonate particles in the presence of the organic substrate are rod-like and ellipse-like particles. The polymorphs were characterized with X-ray diffraction (XRD).     

柠檬酸对萤石和方解石的抑制效果研究

通过单矿物浮选试验、人工混合矿试验、Zeta电位测定、接触角测试及X射线光电子能谱(XPS)测试分析,考察了柠檬酸对萤石和方解石在浮选中的作用机理。结果表明,在油酸钠体系下,柠檬酸对萤石的抑制效果强于方解石,柠檬酸抑制两种矿物受pH值的影响较小。对于萤石和方解石的混合矿,随着pH值的升高,萤石精矿的品位和回收率开始下降。Zeta电位、接触角测试及XPS分析结果表明,萤石比方解石表面电位高,Ca 2p轨道的电子结合能大,更容易与柠檬酸结合。柠檬酸作用后,萤石比方解石电位负移大,接触角降低明显,Ca 2p轨道中Ca-COOR的相对含量占比多。萤石与方解石混合时,随着矿浆pH值的升高,Ca 2p轨道中Ca-CO₃的相对含量占比逐渐升高。     

某复杂多金属矿低尾化综合利用技术研究

矿产资源在选矿过程中产生的大量尾矿,既是资源的浪费,又是环境污染源。因此,开展低尾化乃至无尾化综合利用研究,最大程度提高资源利用率是未来矿产资源开发、利用的必由之路。本文在研究国内某复杂多金属矿综合利用时,通过分析所含矿物的基因属性、赋存状态以及嵌布关系,先后进行了钽铌精矿、方解石精矿、锂精矿、云母精矿、长石精矿、石英精矿共计6个产品的选别回收,实现了除少量泥质、铁屑之外的全产品、无尾化综合利用技术路线,可为以后同类型复杂多金属矿的综合回收提供思路借鉴。     

鄂尔多斯盆地东部奥陶系储层特征及控制因素

鄂尔多斯盆地奥陶系马家沟组沉积时期,由于受中央古隆起及边缘坳陷的制约,处于陆缘盆地环境,储层的溶蚀作用较弱,充填作用较强,空间展布具有强烈的非均质性。这种发育特征宏观上受沉积环境、古沟槽、古水动力条件的制约,微观上受孔隙类型、充填强度以及充填物类型的影响。沉积环境决定了沉积岩的类型,后者是储层发育的物质基础;古沟槽纵横交错,控制着残余溶丘的平面分布;压释水决定着区域充填程度的差异。孔洞充填物质的类型主要包括白云石和方解石,白云石对有效孔隙的保存具有建设性作用,方解石对有效孔隙的保存具有破坏性作用,白云石、方解石混合充填区与古沟槽交切形成的微岩溶地貌相叠合,是今后盆地东部奥陶系勘探的主要方向。     

陕甘宁盆地中部气田白云岩储层孔洞充填物与储集性

本文通过孔洞充填物形成期次，充填矿物类型及地球化学特征的研究，指出有效孔洞的不均一分布控制了陕甘宁盆地中部奥陶夭顶部白云岩的储集性和井孔产气能力。     

水玻璃与磷灰石 方解石作用的溶液化学研究

本文通过浮选实验,ζ-电位与吸附量测定及溶液平衡计算,研究了水玻璃与磷灰石及方解石的相互作用。方解石的溶解度较大,溶解后钙离子浓度较大,水玻璃水解组分HSiO_3及SiO_3~(2-)与方解石表面Ca~(2+)发生化学反应,生成硅酸钙沉淀,硅酸钠在方解石表面的吸附量远大于在磷灰石表面的吸附量。水玻璃使方解石表面负ζ-电位显著增大,在pH>9.5,对方解石有选择性抑制作用。     

Rheological behaviour and related granulometric properties of dense aggregated suspensions during an ultrafine comminution process

The rheological behaviour of calcite suspensions made of particles with different size distributions, obtained by means of a wet comminution process, have been studied versus the operating conditions (volume concentration, use of dispersing agent). The suspension properties (size distribution, specific surface area [SSA]) were investigated in order to characterize the microstructure of the aggregated suspensions. The suspension acts as a thinning fluid with a yield value, and the viscosity increases when the particle size decreases (colloidal dispersions) due to attractive interparticle forces. The use of a polyelectrolyte (sodium polyacrylate [SPA]) during the size-reduction process allows strong reduction of the viscosity of the ground suspensions. The polymer is adsorbed onto the surface of the particles and, consequently, prevents aggregation and allows improvement of the process efficiency.     

The characterisation of paper composite porcelain in a fired state by XRD and SEM

Paper composite porcelain is widely used to produce artistic objects in ceramic art. The aim of this study is to characterise the microstructure and chemical compositions of paper composite porcelain since they determine the material properties. Interaction between paper filler, paper fibre, and the porcelain clay body in its fired state were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The starting materials were kaolin, feldspar, quartz, hybrid copy/print waste paper, and other waste papers. XRD clearly shows that the paper composite porcelain bodies in the fired state mainly consist of α-quartz, mullite, anorthite and amorphous materials in a complex matrix. In the fired state, calcite from the waste paper’s relict interface to kaolinite from porcelain. A transformation to anorthite in the microstructure of paper composite porcelain was indicated. In the microstructure, anorthite tubes were observed as fibrous structures in their fired state.