Flocculation and dispersion of dolomite by acrylate polymers

This paper reports a study of the flocculation and dispersion of suspensions of dolomite by acrylate polymers of various molecular weights.The mechanism by which dispersion of dolomite occurs is interpreted on the basis of experimental results of dispersion tests, zeta potential and polymer adsorption measurements. From these data, it is concluded that electrostatic effects must not be ignored in explaining the behaviour of mineral suspensions.In the specific case of dolomite, the electric charge interactions appear to play a fundamental role and to be mainly responsible for the dispersion effect observed with polymers of low molecular weight (± 10,000). At high pH values (between 9.5 and 11.2), dolomite slimes can be dispersed, although the coverage of the mineral surface by the polymer is limited to 25%. On the other hand, when a polymer of high molecular weight (about 1,000,000) is used, this factor reaches values above 50%.     

5-alkylsalicylaldoximes as collectors in flotation of sphalerite,smithsonite and dolomite in a Hallimond tube

Flotation tests for sphalerite, smithsonite and dolomite were carried out in a Hallimond tube at various pH values and two concentrations of collector.Adsorption of 5-alkylsalicylaldoximes on the surface of minerals was examined and isotherms for 5-butylsalicylaldoxime plotted.It was shown that sorption intensity of 5-alkylsalicylaldoximes on the surface of minerals decreased in the order: smithsonite, sphalerite and dolomite.Relationship between length of aliphatic chain and collecting activity of 5-alkylsalicylaldoximes was investigated in microflotation tests in a Hallimond tube.5-Propylsalicylaldoxime proved to have the best selectivity in flotation for the range of parameters studied, taking the difference in flotation rates of smithsonite and dolomite as a criterion.It was found that modifications of pH value resulted in changes in both adsorption and flotation.     

Thermo-optical detection of defects and decarbonation in natural smithsonite

Natural hydrothermal ZnCO₃ crystal aggregates are nominally anhydrous phases with interfacial water, with substitutional divalent cations and decarbonation c. 300°C. All these common features must be involved during the experimental heating of a thermoluminescence (TL) glow curve up to 500°C: dehydration–dehydroxylation, phase transition and ion transition of point defects in Zn²⁺ positions. A representative specimen of natural smithsonite was analysed by X-ray fluorescence spectrometry, field emission scanning electron microscopy (FESEM) with a chemical probe of energy dispersive spectrometer, high temperature in situ X-ray diffraction, differential scanning calorimetry, differential thermal analyses coupled to thermogravimetry, TL, radioluminescence and high resolution spectra thermoluminescence (3DTL), to gain an overview of the spectra emission and defects linkages modified by heating from room temperature up to 500°C. The ZnCO₃ specimen contains minor amounts of Ca, Cu, Cr, Cd, Pb, Ce, Co, Ni, Mn and Fe. Under FESEM, it displays CaCO₃ clusters and oscillatory zoning distribution with lamellae ranging from Ca_0.11Zn_0.89 to Ca_0.19Zn_0.81. The analytical results suggest assignments of defects and processes to measured 3DTL emission bands, as follows: (1) peak at ~260°C, ~360 nm bonds, breaking during the thermal decarbonation process; (2) peak ~120°C, ~340 nm: non-bridging oxygen centres associated to a complex dehydration–dehydroxylation process and (3) peak at ~170°C, ~650 nm, crystal field effects on the thermoluminescence of Mn²⁺ centres and associated transitional elements in the ZnCO₃ phase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Qualitative analysis of three-dimensional strain using twins in calcite and dolomite

Turner's (1953) technique of locating the compression (C) and tension (T) axes from the known orientations of C-axis and twin pole ([022̄1] in dolomite and [011̄2] in calcite) for each grain yields the orientation of the unique stress system when a great majority of the grains in the rock shows only singlet twins. However, since it assumes the highest possible value for the coefficient of resolved shear stress s₀ (= 0.5), application of the technique to rocks in which a large number of grains show doublet and triplet twins results in great dispersion of the C- and T-axes. In such cases the unique stress system can be established by preparing separate C-axes fabric diagrams for the untwinned grains, grains with singlet twins, grains with doublet twins and grains with triplet twins; measurement of the orientations of the twin planes becomes unnecessary.     

白云石重结晶作用及其地质意义

重结晶作用是白云石形成多期次动态系统中一种常见的成岩后生作用。白云石的成因问题，即“白云岩问题”一直困扰着地质学者，其中一个重要原因是白云岩中白云石的重结晶作用导致白云石形成的原始信息被掩盖，主要包括其结构和地球化学特征的变化。本文在调研国内外有关白云石重结晶作用文献基础上，系统梳理了地质历史时期古老地层中白云石和现代沉积白云石的重结晶作用，以及重结晶模拟实验中白云石岩石学及地球化学变化特征，阐述白云石重结晶的主要条件、影响因素及成岩过程中白云石重结晶作用发生的多期次性及主要变化特征，总结了白云石重结晶作用的研究意义，旨在为“白云岩问题”及成岩作用方面的研究提供一定的借鉴和启示。     

Nanotopography of synthetic and natural dolomite crystals

Examination with scanning electron microscopy (SEM) and scanning force microscopy (SFM) revealed etch pits, layers and islands on dolomite crystal faces synthesized from calcite in Ca‐Mg‐Cl solutions at 200 °C and a wide variety of natural dolomites. Layers are broad, flat structures bounded by steps less than 100 nm high and greater than 1 μm wide. Islands are rounded topographic highs <20 nm high and <200 nm wide. The nanotopography of synthetic dolomite changed from islands throughout most of the reaction to layers at 100% dolomite. Island nanotopography formed on both Ca‐rich and near‐stoichiometric dolomite. Analyses of reaction products from dolomite synthesis indicates that there are no SFM‐detectable products formed in <10 h. SEM‐detectable products formed in 15 h. X‐ray diffraction (XRD)‐detectable products formed in ≈18 h, and the reaction went to completion in ≈40 h. Based on SFM analyses, the induction period for dolomitization in these experiments accounts for ≈20% of the total reaction time necessary to dolomitize CaCO₃ completely under the experimental conditions used here. Island nano‐ topography is inferred to occur at higher degrees of supersaturation than layer nanotopography for three reasons. First, island nanotopography on synthetic calcite and gypsum forms at higher supersaturations than layer nanotopography. Secondly, island nanotopography formed in solutions with higher degrees of supersaturation with respect to dolomite. Thirdly, the greater surface roughness of a crystal face composed of islands compared with layers indicates that island surfaces have higher surface energy than layer surfaces. Therefore, the stability of island surfaces requires a higher degree of supersaturation. Because islands and layers form under a wide range of conditions, their presence provides broadly applicable criteria for evaluating relative degrees of supersaturation under which ancient dolomite formed. Comparison of synthetic dolomites with natural dolomites demonstrates (1) similar nanotopography on natural and synthetic dolomites and (2) both natural planar and non‐planar dolomite may have island nanotopography.     

Structure and reactivity of the dolomite (104)-water interface: New insights into the dolomite problem

The structure and reactivity of the dolomite (104)-water interface was probed in situ with high resolution X-ray reflectivity and surface force microscopy at room temperature. Measurements in stoichiometric solutions alternating between saturated and supersaturated (log IAP/K = 2.3) conditions show that the dolomite surface termination readily changes in response to solution composition, but these changes are self-limiting and partially irreversible. The freshly cleaved dolomite (104) surface in contact with the saturated solution has a stoichiometric termination, a distinct surface hydration layer and small surface structural displacements, similar to those observed previously at the calcite-water interface. After reaction with supersaturated solutions dolomite is terminated by a two-layer thick Ca-rich film with substantial structural displacements of the cations. With subsequent exposure to a saturated solution this surface was transformed to an interfacial structure different from the freshly cleaved surface, having a reduced density of the outermost surface layer and a Ca-rich second layer. These results provide new insight into the lack of dolomite growth in modern carbonate environments (i.e., the “dolomite problem”), suggesting that this behavior is associated with a combination of thermodynamic and kinetic factors, including (1) growth of compositionally modified epitaxial Ca_XMg_2−X(CO₃)₂ layers having thicknesses limited by lattice strain, (2) slow incorporation of Mg during layer growth, and (3) partial irreversibility of surface reactions.     

Precipitation of dolomite using sulphate-reducing bacteria from the Coorong Region, South Australia: significance and implications

Dolomite was successfully precipitated in culture experiments that simulated microbiogeochemical conditions prevailing during late stages of evaporation in ephemeral, hypersaline dolomitic lakes of the Coorong region, South Australia. Analyses of lake- and pore-water samples document rapid geochemical changes with time and depth in both dolomitic and non-dolomitic lakes. Extremely high sulphate and magnesium ion concentrations in lake waters decline rapidly with depth in pore waters throughout the sulphate-reduction zone, whereas carbonate concentrations in pore waters reach levels up to 100 times those of normal sea water. Ultimately, sulphate is totally consumed and no solid sulphate is recorded in the dolomitic lake sediments. ‘Most probable number’ calculations of lake sediment samples record the presence of large populations of sulphate-reducing bacteria, whereas sulphur-isotope analyses of lake-water samples indicate microbial fractionation in all the lakes studied. Viable populations of microbes from the lake sediments were cultured in anoxic conditions in the laboratory. Samples were then injected into vials containing sterilized clastic or carbonate grains, or glass beads, immersed in a solution that simulated the lake water. Falls in the levels of sulphate and rising pH in positive vials were interpreted as indicating active bacterial sulphate reduction accompanied by increased concentrations of carbonate. Within 2 months, sub-spherical, sub-micron-size crystals of dolomite identical to those of lake sediments were precipitated. It is concluded that bacterial sulphate reduction overcomes kinetic constraints on dolomite formation by removing sulphate and releasing magnesium and calcium ions from neutral ion pairs, and by generating elevated carbonate concentrations, in a hypersaline, strongly electrolytic solution. The results demonstrate that bacterial sulphate reduction controls dolomite precipitation in both the laboratory experiments and lake sediments. It is proposed that dolomite formation, through bacterial sulphate reduction, provides a process analogue applicable to thick platformal dolostones of the past, where benthic microbial communities were the sole or dominant colonizers of shallow marine environments.     

喀喇昆仑火烧云深成菱锌矿矿床地质特征及成因

新疆和田火烧云矿床是青藏高原西部新发现的重要超大型矿床之一,是迄今我国规模最大的锌(铅)矿床,同时也是全球罕见的巨型菱锌矿矿床,累计探明铅锌资源储量超过1800万吨,因其经济价值巨大,矿床成因引人注目。详实的野外地质剖面和钻孔岩芯观察证实,容矿围岩龙山组由泥晶灰岩、砂屑灰岩、鲕粒灰岩和生物碎屑灰岩等组成,广泛发育鸟眼构造、窗格构造和平底晶洞构造,指示沉积环境为中侏罗世碳酸盐岩台地滨海—潮坪的滩坝(介壳滩、鲕粒滩)高能环境。矿区已发现上、下两个含矿层,20余个矿体。下含矿层菱锌矿主矿体储量占比超过95%。矿体呈透镜状、似层状产出,小角度穿切围岩地层。矿石矿物以菱锌矿为主,少量白铅矿和方铅矿;脉石矿物以方解石为主,少量石膏。菱锌矿矿石发育交代、自形—半自形结晶结构,块状、晶洞、条带状和斑马状构造。火烧云超大型矿床形成经历了阶段Ⅰ菱锌矿(Sm1)、阶段Ⅱ菱锌矿(Sm2)—(方铅矿)和阶段菱锌矿(Sm3)—Ⅲ方铅矿(铅矾)三个连续成矿阶段,其中主成矿阶段菱锌矿(Sm1)占比80%以上。矿区灰岩及碳酸盐矿物碳—氧同位素分析结果表明,菱锌矿基本继承了主岩灰岩的碳—氧同位素,结合菱锌矿矿石交代结构特征,证实火烧云矿床属于后生热液交代成因。基于菱锌矿矿石矿相学和碳—氧同位素特征,本文首次提出并详细讨论了火烧云矿床的菱锌矿化成矿作用,即富锌少铅贫硫(S~(2-))热液通过微米级方解石溶解—菱锌矿沉淀藕合作用交代龙山组灰岩。因此,火烧云矿床既不是发生氧化的MVT锌矿床,也不是SEDEX锌碳酸盐矿床,而是一类原生深成(hypogene)热液交代锌碳酸盐矿床。     

Selective flocculation of synthetic mineral mixtures using modified polymers

The role of the presence of active groups in polymers and operating variables such as conditioning time in producing flocculation in single and mixed mineral slimes made of hematite, quartz and chalcopyrite is examined at different conditions of pH. Selective flocculation was achieved on the basis of results obtained for single mineral systems as, for example, in the case of hematite—quartz mixtures using sulfonated polymer. Flocculation was found to go through a maximum as the mineral was conditioned with the polymer solution. Interestingly, the times of maximum flocculation for various minerals were sufficiently different from each other so that it could be considered as a potential factor for achieving selectivity. Also, cleaning of the selectively flocculated product by simple redispersion in water improved the separation. Electrokinetic studies conducted to study the mechanisms involved provided indication for the shift of shear plane.     

Dolomitization and the causes of dolomitization dolomite reservoir

This paper utilizes multi-methods,such as core observation,slice identification,isotope analysis,trace element analysis,fluid inclusion technique and so on,to study the causes of the dolomite in the Nanpu Sag and the origins of the dolomite reservoir.The study results show that the forming environment of dolomite in the Nanpu Sag is a fresh-water lake environment,and the dolomite is the product of dolomitization which is caused by volcanic thermal fluids in the Early Dongying period.With the development of intergranular pores in the dolomitization process,a lot of dissolved pores/vugs and fractures were formed by denudation in the later periods because of the influence of thermal fluids including the associated fluids of volcanic activities and the expelled hydrocarbon fluids of the source rocks.On the whole,these secondary dissolution spaces greatly enhance the reservoir ability of the dolomite,and there are enough reservoir spaces in the dolomite in the Nanpu Sag.     

流化床混凝装置中多级速度梯度的建立及其对混凝反应的影响

利用不同性质颗粒在流化状态下可实现自然水力分级的特征,在流化床反应器中沿水流方向实现了多级速度梯度的建立。在研究流化床混凝反应器的混凝动力学特征基础上,探讨了以800 μm和1 200 μm树脂颗粒为固相的多级速度梯度流化床（MGF）的速度梯度分布特征、混凝效率和絮体形态特征,并与以1 200 μm树脂颗粒为固相的单级速度梯度流化床（SGF）进行了对比研究。结果表明：与单级速度梯度相比,多级速度梯度可为胶体或微颗粒的高效碰撞和絮体再增长创造更适宜的环境,有助于形成尺寸更大、密度更大的絮体,提高了絮体的可沉降性;MGF在处理人工配置的高岭土悬浊液和分散红染料废水时,混凝效率比SGF分别提高了2%～4%和7%～20%。     

Flocculation and dewatering of Alberta oil sands tailings

Extraction of bitumen from the oil sands of Alberta with hot water produces a tailing sludge which is very difficult to filter or dewater. The exceptional stability of the sludge is due to the presence of clays, chiefly kaolinite and montmorillonite.Methods of flocculating this sludge have been investigated. Flocculation by an anionic polyacrylamide after pretreatment with optimum concentration of Mg²⁺ or Ca²⁺ ions gave best results.Dewatering of the flocculated sludge by drainage on a sand bed and on a wire mesh has been investigated. Compact flocs carrying < 40% moisture could be obtained.     

The nature of ordering and ordering defects in dolomite

The apparent lack of transformation-induced domains and stacking disorder defects in natural dolomites is considered in light of the different types of order in the dolomite structure. Experimentally produced twin domain boundaries and basal stacking defects are documented in a dolomite using high-resolution electron microscopy and electron diffraction techniques. Results reveal that upon cation ordering to form the dolomite structure, a twin domain is favored over an antiphase domain. The twin domain boundaries closely resemble antiphase boundaries (APB's) and are in contrast for superlattice reflections. However, background contrast within domains is shown to be different when imaged using certain fundamental reflections. The results allow speculation about the nature of ordering at low temperatures. Observations of twin domain boundaries in samples annealed at different temperatures allow estimation of the critical ordering temperature at 1,100°–1,150° C in stoichiometric dolomite.     

Estimation of dolomite formation: Dolomite precipitation and dolomitization

Reactive-transport models are developed here that produce dolomite via two scenarios: primary dolomite (no CaCO₃ dissolution involved) versus secondary dolomite (dolomitization, involving CaCO₃ dissolution). Using the available dolomite precipitation rate kinetics, calculations suggest that tens of meters of thick dolomite deposits cannot form at near room temperature (25-35°C) by inorganic precipitation mechanism, though this mechanism will provide dolomite aggregates that can act as the nuclei for dolomite crystallization during later dolomitization stage. Increase in supersaturation, Mg⁺²/Ca⁺² ratio and CO₃^-2 on the formation of dolomite at near room temperature are subtle except for temperature.This study suggests that microbial mediation is needed for appreciable amount of primary dolomite formation. On the other hand, reactive-transport models depicting dolomitization (temperature range of 40 to 200°C) predicts the formation of two adjacent moving coupled reaction zones (calcite dissolution and dolomite precipitation) with sharp dolomitization front, and generation of >20% of secondary porosity. Due to elevated temperature of formation, dolomitization mechanism is efficient in converting existing calcite into dolomite at a much faster rate compared to primary dolomite formation.     

The control of cathodoluminescence in dolomite by iron and manganese

Variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese (Mn²⁺) as the most important activator, and iron (Fe²⁺) as the main inhibitor of luminescence. Interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages (Cambrian to Cretaceous) and a wide geographical distribution (North America and Europe). Iron and manganese are positively correlated in the dolomites, with the former showing a greater range of variation. Very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm Mn²⁺ is present in highly luminescing samples. The intensity of luminescence is not proportional to the manganese concentration. Iron begins to quench luminescence as its concentration reaches 10,000 ppm. Above that level, luminescence is rapidly lost and total extinction occurs among samples containing more than 15,000 ppm Fe²⁺, regardless of the manganese concentration.     

Comparative study of dissolution rate-determining mechanisms of limestone and dolomite

The dissolution rate-determining processes of carbonate rocks include: (1) heterogeneous reactions on rock surfaces; (2) mass transport of ions into solution from rock surfaces via diffusion; and (3) the conversion reaction of CO₂ into H⁺ and HCO ₃ ⁻ . Generally, it is the slowest of these three processes that limits the dissolution rate of carbonate rock. However, from experiment and theoretical analysis under similar conditions not only were the initial dissolution rates of dolomite lower by a factor of 3–60 than those of limestone, but also there are different dissolution rate-determining mechanisms between limestone and dolomite. For example, for limestone under the condition of CO₂ partial pressures dissolution rates increased significantly by a factor of about ten after addition of carbonic anhydrase (CA) into solution, which catalysed the conversation reaction of CO₂, whereas CA had little influence on dolomite dissolution. For dolomite, the increase of dissolution rate after addition of CA into solution appeared at Moreover, the enhancement factor of CA on dolomite dissolution rate was much lower (by a factor of about 3). In addition, when dissolution of both limestone and dolomite was determined by hydrodynamics (rotation speed or flow speed), especially under the dissolution of limestone was more sensitive to hydrodynamic change than that of dolomite. These findings are of significance in understanding the differences in karstification and relevant problems of resource and environment in dolomite and limestone areas.     

氯化物对方解石和白云石矿物溶解度的影响

借助PHREEQC软件,文章对方解石、白云石分别在无CO2和大气PCO2条件下NaCl、KCl、CaCl2和MgCl2溶液中的溶解度进行了模拟计算,结果显示:方解石在NaCl、KCl、和MgCl2溶液中以及白云石在NaCl、KCl溶液中的溶解度比纯水中大得多,其原因主要是盐效应。由于同离子效应,在CaCl2溶液中可降低方解石溶解度,而白云石在较高浓度CaCl2或MgCl2溶液中,虽发生同离子效应,其溶解度仍较纯水中有不同程度提高。模拟还显示,方解石在MgCl2溶液中以及白云石在CaCl2溶液中溶解时将分别发生白云石化和去白云石化反应,从而促使不全等溶解继续发生。在常规离子中,按方解石、白云石溶解度提高发挥作用的重要性排序为:阴离子中都是SO24->Cl-;对于方解石溶解,阳离子中Mg2+>Na+>K+>Ca2+;对于白云石溶解,当PCO2=0或PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以下时,Na+>K+>Ca2+>Mg2+;当PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以上时,Ca2+>Na+>K+>Mg2+。