The mechanism of ground granulated blastfurnace slag preventing alkali aggregate reaction

Three different methods were applied to study the alkali content of gelpores in cement. In the closed system, the concentration of K⁺, Na⁺ and OH⁻ have not reduced with the increase of age. In the open system, the diffusion and transferring of K⁺ and Na⁺ towards free space leads to the decrease of total alkali content. In the micro-analysis system, the contents of K⁺ and Na⁺ in the first hydrated layer of ground granulated blastfurnace slag (GBFS) are very low, while the contents of calcium and magnesium are relatively high. This phenomenon shows that the mechanism of GBFS preventing alkali aggregate reaction (AAR) is: when GBFS is dissolved by alkali medium, SiO₂ and Al₂O₃ are dissolved into the cement matrix, then around GBFS particles form reaction rings rich in Ca²⁺ and Mg²⁺, and the C-S-H gel of positive charges formed in the area repulses K⁺ and Na⁺, which are forced to transfer to the mortar’s matrix, pore or mortar sample surface. The transferred K⁺ and Na⁺ form alkali gel products with other dissolved ions, then become evenly distributed in the mortar sample and react with Ca(OH)₂ in pore solutions to form (Na,K) _x−2z ·zCa·(SiO₂)_y·(OH)_x gel products; and thus changes the AAR gel products’ structure. The gel products will not expand, and so they can delay expansion destruction.     

HYDROPHOBICITY－HYDROPHILICITY BALANCE RELATIONSHIPSFORCOLLECTORLESSFLOTATIONOFSULPHIDEMINERALS

ＨＹＤＲＯＰＨＯＢＩＣＩＴＹ－ＨＹＤＲＯＰＨＩＬＩＣＩＴＹＢＡＬＡＮＣＥＲＥＬＡＴＩＯＮＳＨＩＰＳＦＯＲＣＯＬＬＥＣＴＯＲＬＥＳＳＦＬＯＴＡＴＩＯＮＯＦＳＵＬＰＨＩＤＥＭＩＮＥＲＡＬＳＨＹＤＲＯＰＨＯＢＩＣＩＴＹ－ＨＹＤＲＯＰＨＩＬＩＣＩＴＹＢＡＬＡ...     

Kinetics of Fe3O4 formation by air oxidation

The kinetics of Fe₃O₄ formation by air oxidation of slightly acidic suspension of Fe(OH)₂ was studied. The effects of initial concentration of Fe(II), temperature, partial pressure of oxygen, air flow rate and stirring rate on the oxidation rate were investigated. The results show that Fe₃O₄ formation is composed of two-step reaction, the first step is the formation of Fe(OH) ₂ ⁺ by oxidation of Fe(OH)⁺ complex ions, the second step is the formation of magnetite by dehydration and deprotonation of Fe(OH)⁺ and Fe(OH) ₂ ⁺ . The oxidation reaction is zero-order with respect to the concentration of Fe(II) and around 0.5-order with respect to partial pressure of oxygen, and oxygen transfer process is rate-limiting step of oxidation reaction with apparent activation energy of 2.74 kJ · mol⁻¹.     

难免离子对中低品位钙镁质磷矿石反浮选的影响

采用浮选试验,结合溶液化学计算、方差分析、扫描电镜和X射线荧光光谱分析等手段研究难免离子对中低品位钙镁质磷矿石反浮选的影响. 研究结果表明:矿浆中Ca²⁺和Mg²⁺会降低浮选磷精矿中P₂O₅含量而提高MgO含量,原因是Ca²⁺和Mg²⁺会沉淀捕收剂解离的RCOO^-,降低其有效浓度;SO₄^2-会降低磷精矿中P2O5回收率,其作用机理是由于SO₄²-能与Ca²⁺作用生成硫酸钙沉淀并覆盖在氟磷灰石和白云石表面,增强氟磷灰石的可浮性,导致氟磷灰石随白云石一起浮出;PO₄^3-对浮选影响较小;Ca²⁺、Mg²⁺、SO₄^2-和PO₄^3-对磷精矿中SiO₂、Al₂O₃和Fe₂O₃含量影响较小. 由于Ca²⁺和SO₄^2-分别对磷精矿P₂O₅品位和P₂O₅回收率影响显著,因此在回水利用过程中需控制矿浆中Ca²⁺和SO₄^2-浓度,降低其对浮选的影响.     

Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend

The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg(NO_3)_2 solutions utilizing ~(29)Si, ~(27)Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg(NO_3)_2 solutions as compared to the pastes cured in water. Moreover, Mg~(2+) ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al~[6] in TAH, respectively. On the other hand, Mg~(2+) ions exert an impact on the intra-transition between Al~[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO_3~-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase(Mg_(1-x)Al_x(OH)_2(NO_3)_x·nH_2O). Results from both ~(27)Al NMR and XRD data show that ettringite seems not to react with Mg~(2+) ions.     

钙镁离子对云南磷矿浮选的影响及回水处理

以云南晋宁、安宁和昆阳磷矿为研究对象,在浮选过程中添加钙镁离子,通过回收率、品位的变化研究其对浮选效果的影响.试验结果表明,当加入的钙镁离子达到一定浓度后,对晋宁和安宁磷矿正浮选有不同程度的影响,而对昆阳磷矿单一反浮选影响不大.同时,晋宁和安宁磷矿正浮选尾矿水钙镁离子的测定结果表明,正浮选尾矿水中的钙镁离子浓度为45 mg/L时不足以影响正浮选过程,正浮选尾矿水可直接返回正浮选;当正反浮选废水混合回用,钙镁离子离子浓度超过100 mg/L时,需处理去除.     

Role of ammonium sulfate in sulfurization flotation of azurite: Inhibiting the formation of copper sulfide colloid and its mechanismOA

In this study, the role of(NH₄)₂SO₄ during the sulfurization of azurite and its response to flotation were investigated. The flotation results showed that adding(NH₄)₂SO₄ prior to sulfurization decreased the formation of colloid in flotation pulp, and the floatability of the suppressed azurite caused by excess sodium sulfide was restored. After adding(NH₄)₂SO₄ prior to sulfurization, the formation ...     

Flotation de-silicating from diasporic-bauxite with cetyl trimethylammonium bromide

1　INTRODUCTIONTheZetapotentialsofkaolinite ,illiteandchlo riteweremeasuredforthecoalflotation ,allthesethreeclaymineralswerenegativelychargedinthepHrangeof 2 .5 11.0 [1] .Theadsorptionofsodiumdode cylsulfateanddodecyltrimethylammoniumchlorideontokaolinitewasstudiedintheabsenceandpresenceofsodiumhexametaphosphate .Itwasfoundthatthepresenceofthelongchainphosphatedecreasedad sorptionoftheanionicsurfactantbutincreasedthead sorptionofthecationicsurfactant[2 ] .Acommercialmonoetheramineandac…     

Growth of covellite crystal onto azurite surface during sulfurization and its response to flotation behavior

In this work, the growth of copper sulfide crystal onto azurite surfaces during sulfurization and its response to flotation are investigated. Filed emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM) and X-ray diffraction (XRD) studies confirmed that the sulfurization of azurite is not limited to the mineral surface, but rather penetrates into the bulk to form covellite crystal (syn-CuS), creating favorable conditions for the stable adsorption of xanthate and greatly promoting the azurite flotation. Additionally, as demonstrated by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS) analyses, a redox reaction occurred during this process, and Cu(Ⅱ) onto the mineral surface was reduced to Cu(I). Correspondingly, reduced S^2- was oxidized to (S₂)^2-, (S_n)^2-, and even to deeper oxidation state S⁰, (S_xO_y)^n- and SO₄^2-. Excess sodium sulfide strengthens copper sulfide to form onto the azurite surface, and provides enough raw material for crystal copper sulfide to grow, resulting in the formation of “flake-like” covellite with a better crystallinity. However, the floatability of azurite decreased dramatically under this condition, because the generated massive colloidal copper sulfide in flotation pulp deteriorates the flotation environment, resulting in a decreased effective adsorption of collector onto azurite surfaces.     

Influence of zinc on electrochemical discharge activity of Mg-6%Al-5%Pb anode

Mg-6%Al-5%Pb (mass fraction) anodes with different contents of zinc were prepared by melting and casting. The electrochemical discharge behavior of these anodes in 3.5% NaCl solutions was investigated by galvanostatic test and electrochemical impedance spectroscopy (EIS). The microstructures and the corroded surfaces of these anodes were studied by scanning electron microscopy (SEM) and emission spectrum analysis (ESA). The phase structures and the corrosion products of the anodes were analyzed by X-ray diffraction (XRD). The results show that zinc promotes the grain refinement of Mg-6%Al-5%Pb anode and makes the average discharge potential of Mg-6%Al-5%Pb anode more negative during galvanostatic test. Mg-6%Al-5%Pb anode with the addition of 1% (mass fraction) zinc has the best electrochemical performance. The activation mechanism of zinc to Mg-6%Al-5%Pb anode is as follows: The hydrolyzation of dissolved Zn²⁺ ions reduces the pH value of the solution near the surface of the anode and accelerates the dissolution of Mg(OH)₂ film; The precipitated Zn(OH)₂ with similar structure as Mg(OH)₂ combines with Mg(OH)₂ film easily and makes it break down.     

Preparation of AgSnO2 composite powders by hydrothermal process

Silver-tin oxide powders were synthesized by the hydrothermal method with Ag（NH3）2^＋ solution and Na2SnO3 solution as raw materials and Na2SO3 as reductant. The precipitation conditions of Na2SnO3 solution and the reduction conditions of Ag（NH3）2^＋ were also investigated. The powders prepared were characterized by differential thermal analysis （DTA）, X-ray diffraction analysis （XRD）, scanning electron microscope （SEM） and energy spectrum analysis, The results show that pH value of the solution is a key parameter in the formation of Sn（OH）4 precipitate and the reduction reaction of Ag（NH3）2^＋ can release H^＋ ions, which results in synchronous precipitation of Sn（OH）6^2- as Sn（OH）4. The reduction of Ag（NH3）2^＋ and precipitation of Na2SnO3 occur simultaneously and the coprecipitation of silver and tin oxide is reached by the hydrothermal method. The silver-tin oxide composite powders have mainly flake shape of about 0.3 μm in thickness and there exists homogeneous distribution of tin oxide and silver in the powder synthesized.     

Reaction products of MgO and microsilica cementitious materials at different temperatures

The paste was prepared by mixing MgO, microsilica and H2O in the presence of water reducer at different reaction ratios and temperatures, and characterized by XRD, DTA, TGA, IR, and solid-state 29Si NMR. The experimental results showed that, besides Mg(OH)2, magnesium silicate hydrate (M-S-H) was formed at a low temperature such as 25 and 50 ℃. At a high temperature of 100 ℃, Mg(OH)2 can be further transformed into M-S-H completely, for instance, within ca. 1 month in an excess of microsilica. The average composition and structure of M-S-H was mainly related to the reaction mixture and curing temperature and was discussed in detail.     

Synthesis of glycerine-xanthate and its depressing mechanism in separation of marmatite from arsenopyrite

A small molecular organic depressor glycerine-xanthate was synthesized. The effect of glycerine-xanthate on the flotation of sulfide minerals was investigated based on a function of pH value and concentration of glycerine-xanthate through flotation experiments in the presence and absence of Cu^2＋. The results show that glycerinee-xanthate has a strong dressing effect on marmatite at pH〉6 and on arsenopyrite in weak acid and base conditions with butyl-xanthate as collector. In the presence of glycerine -xanthate, marmatite is activated by addition of Cu^2＋, but arsenopyrite cannot be activated and remains unfloatable. So the selective separation can be achieved for two minerals. The depression of glycerine-xanthate on sulfide minerals was discussed based on the radical electronegative calculation and the theory of HSAB. Infrared spectrum shows that there are some -OH and-CSS-in glycedne-xanthate molecule, which competes with butyl-xanthate on the mineral surface. As a result of many hydrophilic groups in glycerine-xanthate, the surfaces of marmatite and arsenopyrite become hydrophilic, thus the flotation of marmatite and arsenopyrite is depressed. The collector is adsorbed preferentially on the surface of marmatite and it shows a better floatability in the presence of Cu^2＋, whereas, the surface of arsenopyrite absorbs glycerine-xanthate and the flotation of arsenopyrite is depressed by glycerine-xanthate.     

Flotation performances of polymorphic pyrrhotite

The floatability of different crystalline structures of pyrrhotite (monoclinic and hexagonal) was studied. It is shown that the floatability of monoclinic and hexagonal has obvious difference, and that the flotation recovery of monoclinic pyrrhotite is larger than that of hexagonal pyrrhotite using different collectors. When butyl dithiophosphate is used as the collector, the recovery is larger than that by sodium butyl xanthate and sodium diethyl dithiocarbamate. At the pH values ranging from 6 to 9, monoclinic pyrrhotite can be floated well, and the flotation recovery is higher than 90%. Monoclinic and hexagonal pyrrhotites are more easily activated by Cu²⁺ in acidic conditions than in alkaline conditions. But Cu²⁺ cannot activate hexagonal pyrrhotite using sodium diethyldithiocarbamate as the collector. By the measurement of contact angle, it is indicated that monoclinic and hexagonal pyrrhotites float well and are easily activated by Cu²⁺ when dithiophosphate is used as the collector. Using sodium diethyl dithiocarbamate as a collector, the relationship between potential and pH range for pyrrhotite flotation is established. At pH 5, the optimal potential range for flotation of monoclinic pyrrhotite is about 125–580 mV (vs SHE), with the maximum flotation occurring at about 350 mV (vs SHE); the optimal potential range for flotation of hexagonal pyrrhotite is 200–580 mV (vs SHE), with the maximum flotation occurring at about 300 mV (vs SHE).     

Adsorption of sodium oleate at the microfine hematite/aqueous solution interface and its consequences for flotation

The adsorption of sodium oleate(NaOL) at the microfine hematite/aqueous solution interface was investigated in this paper. Experimental research indicated that negative effects stemmed from the dissolution of the microfine hematite(D50=19.21 μm) could be effectively eliminated via the appropriate dosage of NaOL at alkali pH conditions. Solution chemistry calculation and adsorption test results indicated that RCOO^- and(RCOO)₂^2- ions were responsible for microfine ...     

Effect of pozzolanic reaction products on alkali-silica reaction

1 IntroductionThe use of fly ashto control the expansion dueto al-kali-silica reaction (ASR) is well established and a num-ber of reviews have been published recently[1-4]. Howflyash brings about this reductionin expansionis not yet un-derstood although a number of theories have been put for-ward to explain its action. For controlling mechanism,they put more emphasis onthe adsorption andresort of al-kali by supplementary cementing material (SCM) , formore acidity oxide in SCM,and the secon…     

Insights into the adsorption performance and mechanism of hydrated Ca ion on talc (0 0 1) basal surface from DFT calculation

The utilization of Ca ion as assistant depressant of CMC on talc has been widely reported. Thus, the study on the adsorption mechanism of Ca ion on talc surface is very crucial for understanding the performance of CMC on talc depression. In this paper, mechanism insights into hydrated Ca ion adsorption on talc (0 0 1) basal surface were creatively provided using DFT calculation. [Ca(H₂O)₆]²⁺ and [Ca(OH)(H₂O)₃]⁺ were determined as the effective hydrate components for Ca ion adsorption, and the top O site was the most favorable position for their adsorptions on talc surface. Furthermore, the adsorption mechanisms of [Ca(H₂O)₆]²⁺ and [Ca(OH)(H₂O)₃]⁺ on talc surface were found to be not the Ca—O chemical bond, but the hydrogen bonding formed by the H atom of the H₂O ligand and the surface O atom. H₂O acted like a bridge to connect them to the talc surface. Moreover, the hydrogen bonding was formed due to the hybridization of H 1s orbital with the O 2s, O 2p orbitals. Simultaneously, electrons transferred between the H atom and the surface O atom. This work provides theoretical insights into the Ca ion adsorption on talc surface, which can help deeply understand the talc flotation using CMC as depression.     

Effects of citric acid on hydration process and mechanical properties of thermal decomposed magnesium oxychloride cement

In order to make full use of salt lake magnesium resources and improve the strength of the thermal decomposed magnesium oxychloride cement(TDMOC), the effects of citric acid on the hydration process and mechanical properties of TDMOC was studied. The hydration heat release at initial 24 h and strengths at 3, 7, and 28 days of TDMOC specimens were conducted. The hydration products and paste microstructure were analyzed by XRD, FT-IR and SEM, respectively. The results showed that citric acid can not only reduce the 24 h hydration heat release and delay the occurring time of second peak of TDMOC, but also produce more 5Mg(OH)2·MgCl 2·8H2O and less Mg(OH)2 in hydration process of TDMOC. More perfect and slender crystals were observed in the microstructure of the TDMOC pastes with citric acid. The results demonstrated that citric acid as an additive of TDMOC can decrease the hydration heat release and increase the compressive strength and flexural strength of TDMOC. The possible mechanism for the strength enhancement was discussed.     

Preparation of crystalline Mg(OH)_2 nanopowder from serpentinite mineral

In this paper we describe a route to produce crystalline Mg(OH)2 nanopowders from serpentinite ore distributed in the Halilovskiy array(Russia, Orenburg region). An efficient extraction route consisting of treatment on serpentinite in 40% HNO_3 at 80 °C followed by NH_4OH titration for Mg(OH)_2 precipitation was demonstrated. In this study, crystalline Mg(OH)2 nanopowders have been synthesized by solvothermal reaction method using(Mg(NO_3)_2á6H_2O) which were obtained from serpentinite, NH4 OH as a precipitator, and hydroxyethylated nonylphenol as surface-active substance. Microstructure and phase composition of samples were investigated employing scanning electron microscopy(SEM) and transmission electron microscopy(TEM), X-ray phase analysis(XRD), and inductively coupled plasma optical emission spectroscopy(ICP-OES). XRD reveals that Mg(OH)2 nanopowder with high purity has the brucite structure. It was found that crystalline Mg(OH)_2 nanopowders exclusively consist of lamellar-like structures and the sizes of Mg(OH)_2 are 30–265 nm length or width.     

高效反浮选捕收剂的合成与应用

针对传统脂肪酸捕收剂选择性差、常温下分散性和溶解性差的问题,以工业棉籽油酸为原料,经高温高压使脂肪酸的双键水解而引入羟基活性基团,进一步与助剂按比例复配得到一种高效反浮选捕收剂HY.将其用于宜昌某高镁磷矿的浮选试验,经一反一扫简单浮选工艺流程获得了精矿五氧化二磷品位34.59%,五氧化二磷回收率96.46%,氧化镁品位0.28%的良好浮选选指标,氧化镁脱除率高达95%,各指标优于公开招标各项指标要求,且浮选在常温下进行,药剂用量仅0.84kg/t.表明反选捕收剂HY具有良好的浮选性能,其化学修饰改性改善了捕收剂的常温溶解性同时增强了其对钙离子、镁离子的选择性.