天然黄铁矿除Cr（Ⅵ）中Cr2S3物相的发现

利用天然黄铁矿处理含Cr(Ⅵ)废水实验,在反应中与反应后黄铁矿表面和胶体沉淀物中明显出现Cr2p的XPS能谱峰,能拟合出574.7～575.1eV、576.6～576.9eV和578.2～578.7eV3个峰位,分别代表Cr2S3、Cr2O3和CrO3物相。在实验过程中新发现Cr2S3沉淀物相,表明在常温常压下的水溶液介质中也能产生铬的硫化物物相。充分利用这些含铬物相,能使天然黄铁矿包括天然磁黄铁矿在还原Cr(Ⅵ)的同时,无需加碱就可将Cr(Ⅲ)沉淀转移到胶体沉淀物中,处理后的上清液中全Cr含量低于1.5mg/L的国家允许排放标准。天然黄铁矿自身溶解出的重金属含量很低,不影响处理后的出水水质。开发利用Cr2S3等含铬沉淀物相,便于推广应用天然黄铁矿和磁黄铁矿还原Cr(Ⅵ)同时沉淀Cr(Ⅲ)的一步法除铬新工艺。     

天然含铅黄铁矿试样处理含Cr(Ⅵ)废水的机理研究

天然黄铁矿对Cr (Ⅵ)具有较强的处理能力。本研究选取湖北十堰某天然含铅黄铁矿试样处理含Cr (Ⅵ)的废水,利用X射线衍射、X射线荧光光谱对样品进行结构与成分分析,考察了去除Cr(Ⅵ)反应的影响因素。结果表明,天然含铅黄铁矿样品对Cr (Ⅵ)具有较好的去除能力,其对浓度为50mg/L的含Cr(Ⅵ)废水去除率达95%~99%。并系统研究了黄铁矿颗粒粒度、反应时长、pH值对处理含Cr(Ⅵ)废水性能的影响,发现Cr(Ⅵ)主要吸附在黄铁矿颗粒表面形成絮状物质,对反应后产物的SEM和XRD分析结果表明,反应形成的絮状沉淀物为含铬、铅元素的针状铬铅矿,这对生成次生矿物沉淀从而除铬的新方法具有进一步的研究意义。     

黄铁矿处理含Cr(V)废水的进一步实验研究

利用加热与超细粉碎方法对天然黄铁矿进行改性,探讨其去除Cr(Ⅵ)的效果.将黄铁矿加热到450℃时,试样除Cr(Ⅵ)的效率大幅度增高,适宜的pH范围从小于2.5增加到3.06～11.20,且加热改性的试样用量不到天然试样用量的10%.200目至400目的天然黄铁矿去除Cr(Ⅵ)的效率远较200目以上的天然黄铁矿去除Cr(Ⅵ)的效率高.试样久置不影响对Cr(Ⅵ)的去除效果,去除率可达99.2%以上,反应后的pH值都接近4.0,与磁黄铁矿处理Cr(Ⅵ)废水过程中pH值的变化规律一致.不同产地的黄铁矿样品除Cr(Ⅵ)的效果稍有差异.     

磁铁矿协同增强磁黄铁矿去除水体中六价铬

利用天然磁铁矿辅助合成磁黄铁矿去除水体中的Cr(Ⅵ).实验结果表明,磁铁矿对合成的磁黄铁矿去除水体中Cr(Ⅵ)过程存在协同增强作用.同时利用X射线衍射分析(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)及能谱仪(EDS)对反应前后样品进行分析,发现水体中的Cr(Ⅵ)被有效的还原为Cr(Ⅲ),并以Cr(OH)3及Cr2O3的形式沉淀.设计正交试验探究了磁铁矿粒度、投加量以及废水pH值对除铬过程中2种矿物间协同作用的影响,发现3种因素的影响作用大小顺序为pH值＞磁铁矿粒度＞磁铁矿用量.磁铁矿协同磁黄铁矿去除Cr(Ⅵ)的最优条件为pH值= 3,磁铁矿粒度75～150 μm,用量占比40％.讨论得出2种矿物间的协同作用应包括1)磁铁矿对磁黄铁矿在水溶液中团聚现象的抑制作用;2)酸性条件下磁铁矿表面Fe(Ⅲ)对溶液中磁黄铁矿释放H2S的固定作用.     

单斜与六方磁黄铁矿处理含Cr(VI)废水过程中pH值变化规律

与六方磁黄铁矿相比,单斜磁黄铁矿Fe缺位较普遍。在初始pH值分别为3.40～9.66和3.47～9.66较宽范围内,利用单斜磁黄铁矿和六方磁黄铁矿处理含Cr(VI) 废水,当反应达到充分平衡时,废水的pH值分别变化在3.61～4.47和5.39～6.57范围内。六方磁黄铁矿除Cr(VI)效果明显不及单斜磁黄铁矿,但被氧化的六方磁黄铁矿除Cr(VI)效率有所 提高。电化学分析表明,在酸性介质中处理的反应过程为H+的消耗过程,而在碱性介质中 则为OH 的消耗过程。根据pH值的这一变化规律,可自行调节处理过程中水质的酸性变化 ,能节省传统工艺中需要加碱以中和处理后酸性水的环节,具有一定的实际应用价值。     

黄铁矿处理含Cr(Ⅵ)废水的进一步实验研究

利用加热与超细粉碎方法对天然黄铁矿进行改性 ,探讨其去除 Cr( )的效果。将黄铁矿加热到 4 50℃时 ,试样除 Cr( )的效率大幅度增高 ,适宜的 p H范围从小于 2 .5增加到 3.0 6～1 1 .2 0 ,且加热改性的试样用量不到天然试样用量的 1 0 %。2 0 0目至 4 0 0目的天然黄铁矿去除 Cr( )的效率远较 2 0 0目以上的天然黄铁矿去除 Cr( )的效率高。试样久置不影响对 Cr( )的去除效果 ,去除率可达 99.2 %以上 ,反应后的 p H值都接近 4 .0 ,与磁黄铁矿处理 Cr( )废水过程中 p H值的变化规律一致。不同产地的黄铁矿样品除 Cr( )的效果稍有差异。     

N2气氛下煅烧的黄铁矿对As(Ⅲ)的吸附作用

微量As(Ⅲ)是水中较难去除的毒性物质,天然黄铁矿对水中As(Ⅲ)的去除能力低于磁黄铁矿.将黄铁矿在氮气下高温煅烧使其转变为由磁黄铁矿构成的多孔结构化材料,具有较高的比表面积和表面化学反应活性,在地下水As(Ⅲ)去除方面具有潜在的应用前景.考察了煅烧温度、煅烧时间、pH值以及溶解氧对去除水中As(Ⅲ)的影响.结果表明黄铁矿煅烧生成的单斜磁黄铁矿对As(Ⅲ)具有最佳去除效果,最佳煅烧条件为600℃煅烧1 h;在水溶液有溶解氧条件下煅烧黄铁矿去除As(Ⅲ)的适宜p H值范围较宽(4~10),而在水溶液缺少溶解氧条件下适宜pH值则变为7~10;煅烧黄铁矿在有氧水溶液中对As(Ⅲ)的吸附比缺氧水溶液中的吸附效果好.     

镍钛改性膨润土对铬的吸附性能研究

以钠基膨润土为原料,制备镍钛交联改性膨润土、镍钛有机复合改性膨润土,并应用于含铬模拟废水的处理。探讨了改性膨润土的用量、pH值、吸附时间等最佳使用条件,比较了原土、交联改性土、有机复合改性土对铬的吸附效果。结果表明改性土的吸附效果明显优于原土,在最佳实验条件下,交联改性土、有机复合改性土对Cr(Ⅵ)的去除率分别达到了87%和96%。两种改性土对铬吸附行为均符合Langmuir吸附等温方程,饱和吸附量和Lang-muir常数分别为3.1827mg/g、8.5543mg/g和3.5007、1.2738。     

AMA吸附剂吸附铬(Ⅵ)的性能研究及应用

用凹凸棒石粘土改性制备了AMA吸附剂，对其吸附铬(Ⅵ)的性能进行了较系统地研究。选择了吸附铬(Ⅵ)的最佳条件，用来处理含铬(Ⅵ)废水，铬(Ⅵ)的去除率在96％以上，铬(Ⅵ)的残余浓度小于0．5mg/L，符合国家的排放标准。可以在废水治理中推广应用。     

黄钾铁矾类矿物沉淀去除Cr(Ⅵ)的初步研究

为探讨黄钾铁矾类矿物沉淀对Cr(Ⅵ)的去除效果,利用黄钾铁矾类矿物沉淀对模拟含Cr(Ⅵ)废水进行了初步实验处理,结果表明,黄钾铁矾类矿物沉淀对含Cr(Ⅵ)废水有较好的去除效果,去除率都在70%以上,最高可达85%。黄钾铁矾与黄铵铁矾沉淀对Cr(Ⅵ)的去除率差别不大;溶液酸碱度对去除率有明显影响,在pH值为2.5~3.2时,时间相同,较高的pH值比低pH值的去除率高。黄钾铁矾类矿物的沉淀过程可用来处理矿山及其他工业废水,去除S、Fe和Cr(Ⅵ)等有毒有害元素。     

Elastic and thermoelastic properties of synthetic Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (åkermanite) and Ca<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (hardystonite)

Elastic and thermoelastic constants of large single crystals of Ca₂MgSi₂O₇ and Ca₂ZnSi₂O₇ have been derived from ultrasonic resonance frequencies of plane-parallel plates and their shift upon variation of temperature, respectively. In addition, coefficients of thermal expansion and dielectric constants were determined. Both species possess quite similar properties. As observed in other isotypic magnesium and zinc compounds, the mean elastic stiffness and the deviation from the Cauchy relations are significantly larger in the zinc compound, due to a covalent contribution of the Zn–O bond. Positive thermoelastic constants T₄₄ and T₆₆ in Ca₂MgSi₂O₇ allow temperature-independent ultrasonic generators and oscillators to be manufactured.     

Hydrometallurgical processing and recovery of molybdenum trioxide from spent catalyst

Hydrometallurgical processing of spent hydrodesulphurisation (HDS) catalyst for the recovery of molybdenum using sodium carbonate and hydrogen peroxide mixtures was investigated. The results indicated that the recovery of molybdenum was largely dependent on the concentrations of Na₂CO₃ and H₂O₂ in the reaction medium, which controls the acidity of the leach liquor and carry over of impurities such as Al, Ni, P, Si and V. Leaching process was exothermic and leaching efficiency of molybdenum decreased with increasing solid to liquid ratio. Large scale leaching of spent catalyst, under optimum conditions: 20% pulp density, 85 g/L Na₂CO₃, 10 vol.% H₂O₂ and 1 h reaction, resulted a leaching efficiency of 84% Mo. The obtained leach liquor contained (g/L): Mo — 22.0, Ni — 0.015 and Al — 0.82, P — 1.1, Si — 0.094 and minor quantities of V — 8 mg/L, As and Co — < 1 mg/L. Recovery of Mo from leach solution as MoO₃ of 97.30% purity was achieved by ammonium molybdate precipitation method.     

High-T phase transition of synthetic ANaB(LiMg)CMg5Si8O22(OH)2 amphibole: an X-ray synchrotron powder diffraction and FTIR spectroscopic study

The synthetic amphibole Na_0.95(Li_0.95Mg_1.05)Mg₅Si₈O₂₂(OH)₂ was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P2₁ /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm⁻¹, respectively, and two minor bands at 3,667 and 3,687 cm⁻¹. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (^A□_0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T _c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P2₁ /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ^ANa_0.8^B(Na_0.8Mg_1.2)^CMg₅Si₈O₂₂(OH)₂ indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T _c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.     

地下水中高锰酸盐指数和硝酸根铵根稳定性研究

高锰酸盐指数(CODMn)、硝酸根(NO-3)、铵根(NH+4)是判断水体是否受到三氮污染的重要指标。对于测定这三个指标的水样保存方式和时间,地质行业标准和国内外主要国家标准间存在明显差异。地质行业标准规定地下水样品原水室温保存,CODMn和NH+4在3天内测定;NO-3在20天内测定;国家标准和美国标准推荐样品硫酸酸化,避光或冷藏保存,在2~7天内完成CODMn和NO-3和1~7天内完成NH+4测试。为了分析各类标准在样品保存要求上的差异对检测结果的影响,确保检测数据能真实地反映水体污染状况,找寻简便的保存方式,本文在广州地区采集地下水,按照地质行业标准与国家标准进行处理和保存,并在不同时间段对三个指标进行测试。分析验证结果表明:地质行业标准与国家和美国标准关于水样的保存方法均非常可靠。地质行业标准主要针对静态地下水,保存方法相对宽松;国家标准和美国标准适用范围除了地下水,还包括动态的地表水和废水,采样对象成分更为复杂,更不稳定,更容易受外界影响发生变化,故保存条件高于地质标准。在广州地区,采用原水室温避光保存水样,CODMn、NH+4保存时间可为5天,NO-3保存时间可为30天;采用酸化水室温保存水样,CODMn、NO-3和NH+4保存时间可长达30天。这两种方式均比地质行业标准和国家标准推荐的有效时间长,且原水和酸化水室温保存方式相对于冷藏保存方式更为方便。本文提出,如果采集的水样能方便、快速送达实验室,可采用原水保存;如果不能在短时间内送达实验室检测,可采用硫酸酸化保存。     

硅酸盐玻璃中的Na和K含量电子探针分析条件设定探讨

含Ti硅酸盐玻璃在基础科学研究和应用技术开发上均有重要价值,亟需对其进行准确的成分分析,为进一步的科研工作提供重要的数据支撑.对玻璃进行电子探针分析时,由于样品的易损性和其中(Na和K)阳离子在电子束轰击下极易发生迁移和扩散,因此往往需要经过条件实验来确定合适的分析条件,确保样品在该条件下能够保持尽量稳定的状态,才能获...     

A computer simulation study of OH defects in Mg2SiO4 and Mg2GeO4 spinels

Classical atomistic simulation techniques have been used to investigate the energies of hydrogen defects in Mg₂SiO₄ and Mg₂GeO₄ spinels. Ringwoodite (γ-Mg₂SiO₄) is considered to be the most abundant mineral in the lower part of the transition zone and can incorporate large amounts of water in the form of hydroxyls, whereas the germanate spinel (γ-Mg₂GeO₄) corresponds to a low-pressure structural analogue for ringwoodite. The calculated defect energies indicate that the most favourable mechanisms for hydrogen incorporation are coupled either with the reduction of ferric iron or with the creation of tetrahedral vacancies. Hydrogen will go preferentially into tetrahedral vacancies, eventually leading to the formation of the hydrogarnet defect, before associating with other negatively charged point defects. The presence of isolated hydroxyls is not expected. The same trend is observed for germanate, and thus γ-Mg₂GeO₄ could be used as a low-pressure analogue for ringwoodite in studies of water-related defects and their effect on physical properties.     

Elastic behavior of vanadinite,Pb<Subscript>10</Subscript>(VO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>2</Subscript>, a microporous non-zeolitic mineral

The high-pressure behavior of a vanadinite (Pb₁₀(VO₄)₆Cl₂, a = b = 10.3254(5), c = 7.3450(4) Å, space group P6₃/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V ₀ = 681(1) Å³, K ₀ = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a ₀ = 10.3302(2) Å, K ₀(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c ₀ = 7.3520(3) Å, K ₀(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K ₀(a):K ₀(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe _a (0) = 35(2) GPa for the a-axis, Fe _c (0) = 98(4) GPa for the c-axis and Fe _V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.     

Low-temperature heat capacities of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and spinels of the MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript>–MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> solid solution

We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl₂O₄ and MgCr₂O₄. The data also include new low-temperature heat capacity measurements for MgAl₂O₄ spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed for MgAl₂O₄ spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)₂O₄ spinels. We suggest a standard entropy for MgAl₂O₄ of 80.9 ± 0.6 J mol⁻¹ K⁻¹. For the solid solution between MgAl₂O₄ and MgCr₂O₄, we observe a linear increase of the standard entropies from 80.9 J mol⁻¹ K⁻¹ for MgAl₂O₄ to 118.3 J mol⁻¹ K⁻¹ for MgCr₂O₄.     

Structural changes and valence states in the MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript>–FeCr<Subscript>2</Subscript>O<Subscript>4</Subscript> solid solution series

The influence on the structure of Fe²⁺ Mg substitution was studied in synthetic single crystals belonging to the MgCr₂O₄–FeCr₂O₄ series produced by flux growth at 900–1200 °C in controlled atmosphere. Samples were analyzed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption-, infrared- and Mössbauer spectroscopy. The Mössbauer data show that iron occurs almost exclusively as ^IVFe²⁺. Only minor Fe³⁺ (<0.005 apfu) was observed in samples with very low total Fe. Optical absorption spectra show that chromium with few exceptions is present as a trivalent cation at the octahedral site. Additional absorption bands attributable to Cr²⁺ and Cr³⁺ at the tetrahedral site are evident in spectra of end-member magnesiochromite and solid-solution crystals with low ferrous contents. Structural parameters a₀, u and T–O increase with chromite content, while the M–O bond distance remains nearly constant, with an average value equal to 1.995(1) Å corresponding to the Cr³⁺ octahedral bond distance. The ideal trend between cell parameter, T–O bond length and Fe²⁺ content (apfu) is described by the following linear relations: a₀=8.3325(5) + 0.0443(8)Fe²⁺ (Å) and T–O=1.9645(6) + 0.033(1)Fe²⁺ (Å) Consequently, Fe²⁺ and Mg tetrahedral bond lengths are equal to 1.998(1) Å and 1.965(1) Å, respectively.