Diatomaceous deposits of Fayium, Egypt; characterization and evaluation for industrial application

The Holocene lacustrine diatomaceous earth of Fayium,South West of Cairo,has been studied to define its minerals,chemistry,petrography and physical properties.Minerals were processed by way of calcination at 550℃ ,followed by acid leaching to reduce levels of mineral impurities.The diatomite is of biogenic opal A.with calcite as the main ganue mineral,quartz and clay minerals(smectite followed by kaolinite in abundance and a trace amount of illite).Silica in the diatomaceous earth accounts for about 63% on average.Positive correlation between CaO and CO2 indicates that Ca is present mainly as calcite.Al2O3,Fe2O3,MgO and K2O are attributed mainly to clay minerals.However,the physical properties of the diatomaceous earth as filter-aids and filler for paints and plastics are poor because of general high levels of impurities.The technological performances of the diatomaceous earth have been significantly improved owing to upgrading of diatoms through mineral processing trical.     

硅藻土在一些高附加值产品中的应用及其基础研究

硅藻土是重要的非金属矿物材料。本文综述了它在具有高附加值的功能材料领域,包括助滤剂、吸附剂、载体中的应用,并从这些产品对原料的要求的角度,探讨了有关硅藻土的成分、结构、表面酸性、羟基结构、界面反应性,以及提纯处理的研究现状。     

山东山旺中新世硅藻土的纹层类型及成因

山东临朐山旺地区中新世山旺组硅藻土极为发育。通过对该地区硅藻土纹层的研究,确定其分类和成因,为进一步确立年纹层的存在、利用其进行高分辨率测年、探讨高频古气候旋回奠定基础。山旺组硅藻土的单层纹层厚度一般为100μm左右。依据纹层的物质成分,单层纹层可分为硅藻纹层、有机纹层和粘土纹层三种类型。各类单层纹层组合成为明暗相间的层偶,层偶厚度一般为100～400μm,常常表现为浅色的硅藻纹层逐渐向深色的粘土纹层或有机质纹层渐变过渡。纹层层偶可分为:薄层硅藻纹层-有机质层偶,厚层藻纹层-有机质层偶,薄层粘土纹层-有机质层偶,厚层粘土纹层-有机质层偶和硅藻纹层-粘土纹层层偶。山旺组硅藻土中不同类型的单层纹层以及层偶的形成主要受控于当时湖盆内粘土物质的沉积速率、硅藻的繁盛程度和有机物质的沉积和保存条件。     

膨胀性硅藻土的力学性质及其灾害效应研究

在云南保山－腾冲高速公路建设中,遇到了与膨胀性硅藻土相关的边坡稳定问题。通过对云南腾冲五合乡、芒棒乡、团田乡多个地质剖面现场调查和室内物质成分、微观结构分析、力学性质测试表明,云南腾冲新近纪芒棒组硅藻土是一种富含膨胀性黏土矿物的黏土质硅藻土,在性状上属于膨胀性极软岩。天然硅藻土具有很强的结构性,导致其物理性质与力学性质的关系与传统岩土力学规律极不相符,如孔隙比高达2.20～2.78、液性指数为0.66～2.73的天然硅藻土单轴抗压强度竟高达1.09～2.11 MPa。综合研究表明,云南保山－腾冲高速公路建设中黏土质硅藻土边坡的滑坡灾害、风化剥落灾害与其工程特性密切相关。     

粤西徐闻九亩硅藻土对水体中Zn2+的吸附实验研究

粤西徐闻九亩硅藻土表面多孔,除含有蛋白石外,还含有少量的蒙脱石等粘土矿物;其对水体中的Zn^2＋具有修复能力,且对Zn^2＋的吸附效率较高;宜在弱酸性-中性的pH值条件下修复Zn^2＋;在低Zn^2＋浓度下,硅藻土可以有效地去除Zn^2＋,而对硅藻土进行改性后将有利于对较高浓度的Zn^2＋进行修复;评价硅藻土对水体中Zn^2＋的修复效果应该综合考虑去除率与负载量,在Zn^2＋初始浓度为20mg/L时,徐闻九亩硅藻土吸附剂的用量应以10g/L为宜。     

Chert spheroids of the Monterey Formation,California (USA): early‐diagenetic structures of bedded siliceous deposits

Chert spheroids are distinctive, early‐diagenetic features that occur in bedded siliceous deposits spanning the Phanerozoic. These features are distinct in structure and genesis from similar, concentrically banded ‘wood‐grain’ or ‘onion‐skin’ chert nodules from carbonate successions. In the Miocene Monterey Formation of California (USA), chert spheroids are irregular, concentrically banded nodules, which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite. During shortening, there is brittle fracture of diatomite around, and horizontally away from, the convex surface of strain‐resistant chert nodules. Unlike most older siliceous deposits, the Monterey Formation still preserves all stages of silica diagenesis, thus retaining textural, mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures. Chert spheroids found in opal‐A diatomite form individual nodules composed of alternating bands of impure opal‐CT chert and pure opal‐CT or chalcedony. With increased burial diagenesis, surrounding diatomite transforms to bedded porcelanite or chert, and spheroids no longer form discrete nodules, yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony. Petrographic observations show that the purer silica bands are composed of void‐filling cement that precipitated in curved dilational fractures, and do not reflect geochemical growth‐banding in the manner of Liesegang phenomena invoked to explain concentrically banded chert nodules in limestone. Chertification of bedded siliceous sediment can occur more shallowly (< 100 m) and rapidly (< 1 Myr) than the bulk silica phase transitions forming porcelanite or siliceous shale in the Monterey Formation and other hemipelagic/pelagic siliceous deposits. Early diagenesis is indicated by physical properties, deformational style and oxygen‐isotopic composition of chert spheroids. Early‐formed cherts formed by pore‐filling impregnation of the purest primary diatomaceous beds, along permeable fractures and in calcareous–siliceous strata.     

云南省寻甸先锋盆地中新世褐煤与硅藻土沉积特征

同沉积构造和盆缘古地貌，控制沉积盆地的分布与沉积物的性质。先锋盆地的同沉积断裂与盆内的冲积扇，控制褐煤与硅藻土的分布，也决定着煤与硅藻土的矿物质含量与组分。古气体和水体营养程度的变化，导致出现不属种的硅藻组合带，进一步影响硅藻土的品位。     

中国硅藻土矿床地质特征及成矿大地构造条件

中国硅藻土矿床主要赋存于地洼余动期亚构造层中；在空间上主要分布在我国东部华夏期地洼区和西南部中亚期地洼区。根据游离SiO2来源及成矿作用特征，可划分出火山沉积型及陆源沉积型等两种矿床成因类型。通过成矿大地构造条件分析发现地洼余动期最有利于硅藻土矿床的形成。     

A precisely‐dated lake‐level rise marked by diatomite formation in northeastern Ireland

The intercorrelation of palaeoclimate events from various studies is often hindered by a lack of precise chronological control. Tephra isochrons can overcome this problem by providing direct site linkages. This paper outlines a study of Holocene peat and diatomite deposits that accumulated within the floodplain of Lough Neagh, Northern Ireland. The Icelandic Hekla 4 tephra has been identified at the base of diatomite deposits at a number of sites and provides firm dating evidence for a widespread flooding event in the area at ca. 2300 BC . The evidence is consistent with other studies in Ireland and elsewhere for increased wetness at this time. The results demonstrate that the terrestrial deposits around Lough Neagh contain an important record of Holocene lake‐level change. Dendrochronological evidence from the Lough Neagh area provides additional information about lake‐level fluctuations over the past two millennia. Copyright © 2004 John Wiley & Sons, Ltd.     

长白山硅藻土热处理相变及方英石形成机制探讨

在常温到1250℃温度范围对吉林长白山硅藻土和非晶态SiO2进行热处理,并对热处理后的样品进行红外光谱和X射线衍射测试,结果表明长自山硅藻土在1100℃开始转变成方英石,非晶态SiO2在1200℃开始形成方英石,它们的转变温度均处于鳞石英的热力学稳定区。方英石这种热力学亚稳态形成机制与硅藻土和非晶态SiO2的中程有序结构与方英石结构类似有关,这种结构相似性有利于降低了方英石成核所需的活化能从而有利于方英石成核作用的发生,因而在硅藻土(非晶态SiO2)→方英石→鳞石英的系列转变反应中,硅藻土→方英石的反应占主导,而在相应的温度条件下,方英石→鳞石英的相变几乎是被禁止的。长白山硅藻土与非晶态SiO2转变成方英石存在大约100℃的温度差异,主要与硅藻土独特的结构缺陷及Na、Al等杂质元素存在有关。高温下Si-OH基团的脱水反应使硅藻土结构中以OH^-形式存在的非桥氧变成桥氧,原来的结构缺陷消失,有利于降低方英石的形成温度;而Na、K、Ca、Fe等杂质元素与SiO2形成多组份体系,导致SiO2结晶温度降低,它们强的扩散特性,还有利于提高孤立Si-OH基团的脱失速率和缺陷迁移速率,并增加方英石的稳定性。