Impact of gypsum on flotation of scheelite and fluorite using sodium oleate as collector

ABSTRACT

In this study, effect of calcium and gypsum on scheelite and fluorite was investigated using sodium oleate as collector. Micro-flotation and contact angle results showed that the adsorption of calcium could inhibit the hydrophobicity of scheelite and fluorite. Moreover, sulfate could enhance the inhibition. FT-IR results showed that calcium could be priori precipitated into calcium oleate and adsorb on mineral surface. The adsorption of calcium could increase the scheelite potential to IEP, while it showed limited effect on fluorite potential. However, the interaction of calcium on scheelite and fluorite in gypsum solution was more complex than that in calcium solution.     

Formation and reactivity of oxides and basic salts. II. Radio-isotope studies of some calcareous materials

Rates of calcium exchange between solid and solution in the ageing of hydrated lime and of calcium carbonate samples have been determined using calcium-45 radio-isotope. After a comparatively rapid calcium uptake of about 1 molecular layer at the hydrated lime surface, the exchange rate diminishes as the ions need to diffuse more deeply into the hydrated lime structure. Results for calcium carbonate samples of widely different specific surfaces are compatible with very slow ageing in water. Rates of gypsum precipitation from radioactive calcium chloride and nitrate solutions have been compared in neutral and acidic media and in the presence of albumen. Lower gypsum saturation ratios are established ultimately in neutral rather than acidic media, particularly in solutions containing no salts other than gypsum. Solid hydrated lime reacts rapidly with dilute sulphuric acid, aluminium and magnesium sulpnates, magnesium chloride or sea-water, releasing calcium ions into solution. The radioactivities of the solutions decrease subsequently as gypsum separates out or calcium ions are adsorbed by the finely-divided magnesium hydroxide precipitated. At higher magnesium salt concentrations, the calcium-45 radioactivity does not initially increase so sharply. This is ascribed to basic salt formation preventing all of the lime from going quickly into solution.     

钙芒硝石膏深度提纯工艺的研究

钙芒硝石膏是工业上采用溶浸法生产元明粉的副产尾矿,与脱硫石膏和磷石膏等工业副产石膏相比其杂质含量高、纯度低、利用价值低。采用酸浸-重结晶工艺对钙芒硝石膏进行提纯,通过酸浸去除钙芒硝石膏中的酸溶性杂质,并将二水硫酸钙（DH）脱水转化为无水硫酸钙（AH）,然后控制水化条件,使AH水化为大尺寸的DH晶体,并与小尺寸的酸不溶性杂质分离开来,得到高纯度的二水石膏。研究了硫酸浓度、水化激发剂、液固质量比、反应时间等对石膏提纯的影响。研究结果表明：常压下,在硫酸酸洗液质量分数为35%、反应温度为80 ℃、石膏与硫酸溶液固液质量比为1∶5、酸洗时间为2 h时能有效去除钙芒硝石膏中的酸溶性杂质;在水化硫酸质量分数为5%、硫酸钾质量分数为1.74%、反应温度为25 ℃、固液质量比为1∶6、陈化时间为18 h时能有效去除钙芒硝石膏中酸不溶性杂质,提纯后的石膏纯度可达97%以上。     

Utilization of sodium humate as selective depressants for calcite on the flotation of scheelite

The flotation separation of scheelite from calcite using sodium humate (SH) as a potential depressant has been studied through micro-flotation experiments, zeta potential and Fourier transform infrared (FT-IR) spectra measurements. The flotation results indicate SH exhibited selective depression effect on calcite in the presence of sodium oleate, achieving the flotation separation of scheelite from calcite. Zeta potential results indicate that SH strongly absorbed on calcite surface but negligibly on scheelite surface, which prevents the adsorption of sodium oleate on calcite surface. The FT-IR results also show that SH can be adsorb on the surface of calcite. Results shown a higher Ca density on the calcite than on scheelite surface, and that calcite can accommodate the interaction of SH.     

Reactivity of lime and related oxides. XVII. Sulphating of lime with magnesium and aluminium sulphates

Lime water and solid hydrated lime have been sulphated with magnesium and aluminium sulphate solutions. Changes in phase composition and sulphating rates are followed from pH (glass electrode) and conductivity measurements. The crystallinities of the products have been compared with calcium sulphate dihydrate precipitated directly from solution by double decomposition and subsequently aged. The reactions with the solid hydrated lime are not appreciably impeded by the insoluble products, magnesium and aluminium hydroxides, which are very finely divided. These compounds provide additional surface on which most of the gypsum can form a gel when the gypsum solution saturation ratios have become sufficiently high. The small amounts of gypsum ultimately separating out from the lime water have crystallinity inferior to the larger amounts formed from the solid hydrated lime. Both are still inferior to gypsum from acid-sulphated lime, and are more comparable with gypsums precipitated from calcium nitrate in acidic media containing concentrations (±0.1 %) of albumen, or from calcium chloride in neutral media. Slower gypsum precipitation from calcium chloride with sulphuric acid (as in the manufacture of ‘Pearl hardening’) gives a more consistent degree of crystallinity.     

水溶性P2O5对石膏碳酸铵转化过程影响的研究

以纯CaSO4·2H2O添加水溶性P2O5进行了石膏与碳酸铵溶液转化反应实验,探索了水溶性P2O5对转化过程的影响及影响机理.实验结果发现,石膏中水溶性P2O5的存在使SO42-的转化率降低,过滤困难,产物具有触变性.X射线衍射、扫描电镜分析表明,水溶性P2O3存在降低了碳酸钙晶型由球霞石向方解石转变的速率,并使碳酸钙晶体晶习变坏.用电子探针和等离子发射光谱分别对产物固相表面成分和滤液中Ca、P含量进行了分析,水溶性P2O5是通过吸附在固相产物表面对碳酸钙晶型和晶习产生影响的.     

Kinetics of Tricalcium Aluminate and Tetracalcium Aluminoferrite Hydration in the Presence of Calcium Sulfate

Hydration reactions of C₃A and C₄AF with calcium sulfate hemihydrate and gypsum were investigated and the kinetics of the reactions compared. The rates of C₃A and C₄AF hydration, as determined by heat evolution, vary depending on whether the sulfate-containing reactant is gypsum or calcium sulfate hemihydrate. The following sequence of reactions involving C₄AF occurs when hemihydrate is the reactant: gypsum formation during the first hour, ettringite formation between 20 and 36 hours, and the conversion of ettringite to monosulfate over a period of about 12 hours. Monosulfate formation initiates prior to the complete consumption of gypsum. The onset of this conversion occurs at a shorter hydration time when hemihydrate is a reactant and the total amount of heat evolved is lower. The hydration reactions in saturated calcium hydroxide solution occur more slowly than those in water. Based on heat liberation, C₄AF reacts at a much higher rate than C₃A. Ettringite formation occurs during the first 8 to 9 days of C₃A hydration. Once the gypsum is consumed, ettringite converts to monosulfate during two additional days. Compared to gypsum, hemihydrate decreases the rates of hydration of both C₃A and C₄AF. The effects on the hydration characteristics of C₄AF are significant. The hydration of C₃A with gypsum in water, in saturated Ca(OH)₂ solution, and in 0.3 M NaOH solution were compared. Heat evolution is the lowest for hydration in 0.3 M NaOH. The onset of monosulfate formation occurs prior to the complete reaction between gypsum and C₃A in the NaOH solution.     

The combined effect of lead ion and sodium silicate in the flotation separation of scheelite from calcite

Flotation separation of scheelite from calcite is difficult because of the existence of the same cation in the minerals and similar physicochemical characteristics. Many studies have been performed to determine the selective depressants for calcite, but the separation of scheelite from calcite is still a big problem. In this article, the flotation separation of scheelite from calcite has been studied by flotation tests. The results show that benzohydroxamic acid has weak collecting ability to both scheelite and calcite. Lead ions can activate the flotation of scheelite and calcite, but the flotation separation of scheelite from calcite can’t be realized. The depressant saline sodium silicate (mixture of sodium silicate and lead ions) has selective depression effect on calcite and the optimum ratio of sodium silicate to lead ions is 3:1. The use of saline sodium silicate as a depressant can achieve the flotation separation of scheelite from calcite. The zeta potential results and adsorption studies showed that the pre-adsorption of saline sodium silicate only interferes with the adsorption of benzohydroxamic acid on calcite surface; this is the main reason for the selective depression effect of saline sodium silicate on calcite.     

Adhesion of air bubbles to a fluorite surface in the presence of oleate species

Measurements of the detachment force of air bubbles from a surface of fluorite covered with an oleate film immersed in an aqueous sodium oleate solution or water were carried out. The contact angles for the systems fluorite/oleate film-drop of aqueous sodium oleate solution-air, fluorite/oleate film-air bubble-aqueous sodium oleate solution, and fluorite/oleate film-air bubble-water were also measured. The detachment forces were also calculated from the measured contact angles. It was found that the adhesion of air bubbles to the fluorite surface increased considerably in the presence of an oleate film on the fluorite surface, but decreased if the oleate film was at the water-air interface. Good agreement between the theoretically calculated and the measured values of the detachment force for the system fluorite/oleate film-air bubble-sodium oleate aqueous solution when the concentration of this latter solution was in the range 0 to 87.1 mg/dm³ was also found, but for concentrations over 87.1 mg/dm³ the calculated values of the detachment force were higher than the measured values. The calculations and measurements indicate that the most favourable condition for the adhesion of air bubbles to fluorite grains is the presence of a chemisorbed film of oleate without surface precipitation of calcium oleate salt at low concentrations of oleate species in water.     

Impact of zeta potential of early cement hydration phases on superplasticizer adsorption

The zeta potential of early hydration products of cement was found to be a key factor for superplasticizer adsorption. A highly positive zeta potential results in a strong superplasticizer adsorption whereas a negative zeta potential does not allow adsorption. Synthetic ettringite precipitated from solution shows a highly positive zeta potential, hence it adsorbs great amounts of negatively charged superplasticizer. Monosulfate (AF_m) has a less positive zeta potential. Therefore, it adsorbs smaller amounts of superplasticizers. For syngenite, portlandite and gypsum, the zeta potential is around zero or negative. These phases do not adsorb superplasticizers. Consequently, a hydrating cement grain is best represented by a mosaic structure, with superplasticizer molecules mainly adsorbed on ettringite and some on monosulfate and C-S-H nucleated at surface.     

The gypsum reduction process and its validation using the Mintek Pyrosim model

Waste gypsum is produced as a by-product from the fertilizer, mining industries, and acid mine water neutralization using calcium carbonate and/or lime and desalination processes using reverse osmosis and ion-exchange processes, resulting in environmental and storage problems. The purpose of the study was to establish optimum operating conditions for the recovery of valuable products, e.g., sulfur and precipitated calcium carbonate, from waste gypsum, hence, offer an attractive solution to the gypsum waste problem. The paper presents results on thermal studies of waste gypsum in a tube furnace and its validation using the Mintek Pyrosim model. Gypsum was homogeneously mixed with coal and the reduction experiments conducted. The following findings were made: (i) reduction of waste gypsum is an endothermic reaction since, ΔH values were greater than 0 (ΔH?>?0) when the reduction temperature was increased from 25 to 1200°C, (ii) energy requirement is dependent on temperature and gypsum to coal ratio. Gypsum to calcium sulfide conversion of 83.5 and 83.8% was obtained at the optimum temperature range of 1100–1200°C and gypsum to calcium sulfide conversion of 85.4% was obtained at the optimum coal to gypsum mole ratio of 2.1:1, (iii) excess coal gave a lower conversion, and (iv) the predicted data using Mintek Pyrosim were found to be similar to the experimental data.     

增钙煤矸石的结构特征及其活化机理研究

对原样煤矸石进行了系统分析.通过X射线衍射(XRD)和核磁共振(NMR)等测试方法对其活化过程的微观结构进行了分析.结果表明:在煤矸石的增钙煅烧过程中掺入适量的石膏和萤石等组分作为矿化剂时,有水硬性矿物生成.此状态的煤矸石中29Si峰产生了裂解和宽化,铝氧多面体结构由原样中的六配位为主转变为以四配位为主,这样的结构有利于改善煤矸石的活性.对煤矸石活化过程进行了力学性能试验.试验结果同样表明:各种增钙煅烧煤矸石的力学性能和微观结构的分析结果是相一致的.     

Research on cementitious behavior and mechanism of pozzolanic cement with coal gangue

In this paper, the mechanical property of coal gangue in the activatory process is studied by using the method of orthogonal experiment, and then the micromechanism of various coal gangues is determined by modern test methods such as scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The experiment can approve those results: when proper amount of gypsum and fluorite were taken as for mineralizer in the course of calcinations of added-calcium coal gangue, much micropore can appear in microstructure and it can be in more molten state; spectrum peak of ²⁹Si in this kind of coal gangue is not only in splitting decomposition, but also in broadening; the mechanical property of coal gangue calcined with calcium is in accordance with microstructure.     

Effect of the gypsum state in industrial cements on the action of superplasticizers

The reduction in mixing water of the concrete, caused by the addition of a superplasticizer, depends also on the type of cement used. Superplasticizer based on naphthalene sulfonated polymer acts much more effectively on cement containing gypsum dihydrate than on that containing calcium sulfate hemihydrate. Moreover, an improvement of the superplasticizer quality caused by ultrafiltration of the polymer, is more effective on the cement containing gypsum than on that with hemihydrate.     

A Novel Evaluation Method for the Particles Interaction between Sphalerite and Silica

In this paper the particle interactions between sphalerite and silica were studied by zeta potential measurements and a novel zeta potential distribution measurement (ZPD) method in different concentrations of calcium ion solution. The flotation reagent adsorbed on the mineral surface was analyzed by the interaction behavior. The results show that adsorption of flotation reagent is not conducive when the calcium ion concentration is high in the solution. The interaction of mineral particles decreased with the reduction of calcium ion concentration which was favorable for reagent selective adsorption. The mineral interactions can be interpreted by the novel zeta potential distribution measurement (ZPD) method.     

Interactions Between Sodium Oleate and Polyoxyethylene Ether and the Application in the Low-Temperature Flotation of Scheelite at 283 K

The poor collecting performance of fatty acids at low temperatures is a problem in mineral flotation. In this study, the floatability of scheelite at 283 K was studied using sodium oleate and binary mixtures of sodium oleate and lauryl alcohol polyoxyethylene ether (MOA-9) as the collector, and interactions between the two surfactants at 283 K were investigated by the means of surface tension and steady state fluorescence measurements. The flotation experiment results show that the collecting performance of the mixed anonic/nonionic collector is stronger than that of single surfactant, and the best molar ratio of sodium oleate to MOA-9 is 10:1 at pH 10. The surface tension results show that the critical micelle concentration value of sodium oleate, MOA-9 and the binary solution is about 2 × 10^?4, 2.5 × 10^?4, and 1.2 × 10^?4 mol/l, respectively. Compared with single surfactants, the mixture exhibits better surface activities since it is more efficient at decreasing the air–water surface tension. The steady state fluorescence results indicate that the hydrophobic parts of MOA-9 molecules insert into the hydrophobic region of sodium oleate micelles to form larger and less compact mixed micelles. The decrease in zeta potential of scheelite treated with the mixed collector indicates the presence of MOA-9 can enhance the chemical adsorption of sodium oleate on the scheelite surface. Therefore, the mixed anonic/nonionic collector can enhance the flotation behavior of scheelite at 283 K.     

增钙煅烧煤矸石的活性评价及其作用机理

采用增钙煅烧方式活化煤矸石,添加石膏和萤石作矿化剂。对各试样进行游离氧化钙、X射线衍射和核磁共振分析,进一步探讨煅烧过程中矿物组分与微观结构的变化。结果表明：掺加的氧化钙被大量吸收。在一定温度范围内,煅烧煤矸石的硅氧四面体聚合状态发生明显变化,同时生成多种硅酸钙盐矿物。随温度升高,硅氧四面体结构从高聚态向低聚态转变,并伴随生成大量玻璃态和无定型物质,这些物质均有利于改善煤矸石的胶凝活性。     

Effect of clays and calcium ions on bitumen extraction from athabasca oil sands using flotation

A novel approach, based on the doping of rich estuarine oil sands with calcium and/or clays, was developed to study bitumen extraction. The batch flotation tests showed that the addition of either calcium ions up to 40 p.p.m., or kaolinite, illite and montmorillonite clays at 1 wt% of oil sands processed had marginal effect on bitumen recovery from the estuarine ores. A sharp reduction in bitumen recovery was observed only when calcium ions greater than 30 p.p.m. and 1 wt% montmorillonite clays were added together. While bitumen recovery correlated well with changes in water/air/bitumen contact angle, no correlation was found between bitumen recovery and measured zeta potential of clays or surface tension of the supernatants from the flotation slurry. The wettability of bitumen was identified as a key element in determining bitumen recovery. The aqueous solution analysis for calcium ions showed that most of the added calcium ions disappeared from the solution when montmorillonite clays were present. The addition of illite or kaolinite clays changed the calcium ion concentration in the slurry only marginally. Stronger adsorption of calcium ions on montmorillonite than on either kaolinite or illite is considered to be responsible for the increased bitumen wettability, and hence reduced bitumen recovery.     

磷石膏制备硫酸钙晶须的工艺研究

采用常压酸化法对磷石膏分别进行硫酸除杂和盐酸溶解,将磷石膏中的钙富集于溶解液中.再对溶液进行处理制备硫酸钙晶须,考察硫酸钙初始浓度、结晶温度及添加助晶剂种类和用量对硫酸钙晶须组成、结构和形貌的影响.实验结果表明:所制晶须均为二水硫酸钙晶须;以乙醇作为助晶剂所制备的晶须形貌最好.当乙醇的添加量为15 mL(即V乙醇∶V盐酸=1∶2)时所制备的晶须比较均一,平均直径为25 μm,平均长径比约为80.     

Expansion mechanisms in calcium aluminate and sulfoaluminate systems with calcium sulfate

The long-term expansion of calcium aluminate cement and calcium sulfoaluminate cement in the presence of added gypsum has been studied for samples cured under water. Progressively higher amounts of gypsum were added to the CAC or CSA and it was found that there is a critical amount of gypsum leading to unstable expansion and failure of the samples. The microstructures of systems with gypsum additions just below and above the threshold were similar. Pore solution analyses showed that supersaturation with respect to ettringite increases with the calcium sulfate content, which results in an increase of the crystallization pressure. The supersaturation determines the minimum pore size in which crystals can grow. Therefore with higher supersaturation a larger pore volume is accessible to growing ettringite crystals exerting pressure in the porous skeleton. This could explain the critical amount of gypsum leading to high unstable expansion.