醋酸——醋酸铵缓冲体系中柠檬酸对高岭石的溶解特征

采用间歇法(batch method)模拟研究醋酸-醋酸铵缓冲体系中柠檬酸对高岭石的溶解特征。结果表明:反应液中Al、Si浓度随柠檬酸浓度提高、反应液pH降低及反应时间的推移而增加;且低浓度柠檬酸(1mmol L-1)时,随着酸度的升高,配体促进溶解速率(RL)减小;高浓度柠檬酸(≥5mmol L-1)时,随着酸度的升高,配体促进溶解速率(RL)增加,但增幅随pH的降低而大幅减弱;且随着酸度的升高,配体对高岭石溶解的贡献相对减弱,但相对于质子,本试验柠檬酸浓度及酸度范围内,其对高岭石溶解的贡献仍是主要的。     

不同改性黏土矿物吸附净化磷污染水体的性能比较

比较了酸、热及其复合改性对凹凸棒石黏土、膨润土和高岭土等3种黏土矿物吸附净化不同程度磷污染水体能力的影响。结果发现,2%浓度酸处理、300℃热活化及酸热复合改性均可以显著提高凹凸棒石黏土的磷吸附净化能力,且以复合改性效果最好,Ⅴ类和劣Ⅴ类水的磷去除率均比原土提高30%以上;酸、热改性均能显著提高膨润土的磷吸附净化能力,但综合不同程度磷污染水体来看,热活化略优于酸改性,但酸热复合改性没有呈现更佳的效果;热改性显著提高高岭土的磷吸附净化能力,而酸改性却不同程度地降低了高岭土的磷吸附净化能力,酸热复合改性的效果亦不如热单独改性。结果表明,在针对不同程度磷污染水体时需根据黏土矿物特性选用酸处理、热活化或酸热复合改性方法来提高污水的吸附净化效率。     

Differential weathering of granitic stocks and landscape effects in a Mediterranean climate,Southern Iberian Massif (Spain)

Mineralogical and structural features control the weathering processes and landform development of two different crystalline stocks in the Iberian Massif, Spain (the Santa Elena and Linares stocks). The Santa Elena stock shows irregular saprolite profiles and boulder landforms whereas the Linares stock develops broad and plain landscapes with uniform saprolites and less boulder forms. The Santa Elena stock is more closely jointed and fractured than the Linares body. The main secondary minerals are kaolinite, and illite; illite/smectite interstratification was only observed in deep samples from the Linares profile. The Linares profile is feldspar-enriched whereas in Santa Elena plagioclase is almost absent and clay mineral content, especially kaolinite, is higher. Feldspars show dissolution channels developed along cleavage planes filled by clay minerals. Biotite–kaolinite intergrowths have fanned-out textures of epitaxial disposition. Weathered materials are enriched in Al and H₂O and Fe, and depleted in Ca, Na, Mg, Ti, P. The Santa Elena weathered materials are richer in H₂O than those from Linares and have lower Si/Al ratios. Mineralogical and geochemical evidence indicate the Santa Elena materials are more intensely weathered. High fracturation and high Ca-richer plagioclase contents are key factors producing the pervasive Santa Elena stock weathering. Fluvial erosion removed the alteration products in incised tectonically controlled streams resulting in boulder accumulation.     

除草剂草甘膦在几种土壤和矿物上的吸附研究

通过批平衡实验考察了草甘膦在几种性质不同土壤和矿物上的吸附行为。研究发现土壤对草甘膦有较强的吸附能力，草甘膦在土壤上吸附量的大小与土壤理化性质密切相关。草甘膦在土壤和矿物上的吸附符合Freundlich吸附方程，其在土壤上的吸附常数K与土壤粘粒含量呈正相关，并随土壤氧化铁和氧化铝含量增加而增加，而与土壤的pH呈显著负相关。草甘膦在高岭石上的吸附量要比在蒙脱石上大，而草甘膦在金属离子饱和的蒙脱石和高岭石上的吸附研究结果表明，草甘膦在钠、钙、铁离子饱和的矿物上的吸附能力依次为Fe-蒙脱石〉Ca-蒙脱石〉Na-蒙脱石和Fe-高岭石〉Ca-高岭石〉Na-高岭石。     

Adsorption and desorption of monomeric Bt (Bacillus thuringiensis) Cry1Aa toxin on montmorillonite and kaolinite

Genetically modified crops, which produce pesticidal proteins from Bacillus thuringiensis, release the toxins into soils through root exudates and upon decomposition of crop residues. Although the phenomena of gene transfer and emergence of resistance have been well documented, the fate of these toxins in soil has not yet been clearly elucidated. The aim of this study was to elucidate the adsorption and the desorbability of the Cry1Aa Bt insecticidal protein in contact with two sodium-saturated clays: montmorillonite and kaolinite. Because the toxin is released into soil in small quantities, it was assumed that it will be in a monomeric state in solution until it oligomerized on cell membranes. The originality of this study was to focus on the monomeric form of the protein. Specific sample conditions were required to avoid polymerisation. A pH above 6.5 and an ionic strength of at least 150 mM (NaCl) were necessary to keep the protein in solution and in a monomeric state. The adsorption isotherms obtained were of the L-type (low affinity) for both clays and fitted the Langmuir equation. The adsorption maximum of the toxin, calculated by the Langmuir nonlinear regression, decreased with increasing pH from 6.5, which was close to the isoelectric point, to 9. At pH 6.5, the calculated adsorption was 1.7 g g⁻¹ on montmorillonite and 0.04 g g⁻¹ on kaolinite. Desorbability measurements showed that a small fraction of toxin could be desorbed by water (up to 14%) and more by alkaline pH buffers (36 ± 7%), indicating that it was not tightly bound. Numerous surfactants were evaluated and the toxin was found to be easily desorbed from both clays when using zwitterionic and nonionic surfactants such as CHAPS, Triton-X-100, and Tween 20. This finding has important implications for the optimization of detection methods for Bt toxin in soil.     

流动电位法研究高岭石胶体对包铝石英砂zeta电位的影响

为探讨采用流动电位法表征带电颗粒间相互作用的可行性,采用自制的流动电位测量装置测定了高岭石胶体流经包铝石英砂时zeta电位的变化(Δζ),研究高岭石与包铝石英砂之间的作用程度,考察了包铝程度、介质离子强度和离子种类对带电颗粒之间相互作用的影响。结果表明,可采用流动电位法表征不同尺寸的异电荷颗粒间的相互作用。随着石英砂表面包铝程度的增加和介质离子强度的降低,包铝石英砂的Δζ增加,说明其与高岭石之间的作用程度增加。含低价态离子的溶液中高岭石胶体与包铝石英砂的作用程度大于其在含有高价离子的溶液中。采用经典的DLVO理论计算得到的高岭石胶体与包铝石英砂间的作用能可以很好地解释高岭石对包铝石英砂表面电化学性质的影响,两种异电荷颗粒间的静电引力大小是决定高岭石与包铝石英砂间作用程度的关键因素。在静电力的作用下,高岭石通过电荷屏蔽作用和双电层重叠作用改变包铝石英砂的zeta电位。高岭石与包铝石英砂间的静电引力越大,高岭石对包铝石英砂表面电化学性质的影响越大。     

饱和多孔介质中高岭石胶体和SiO2胶体运移行为比较

胶体在多孔介质中的运移行为不仅取决于胶体本身的性质,同时还受到溶液离子强度、孔隙水流速等物理、化学因素的影响。本文通过室内饱和石英砂柱出流实验,探讨了高岭石胶体(Kaolinite胶体)和SiO2胶体在不同离子强度(0.001 5,0.01和0.03 mol L-1)和平均孔隙流速(约20和5 cm h-1)作用下的迁移行为。结果表明,随溶液离子强度增加,Kaolinite胶体和SiO2胶体的沉淀量增加;平均孔隙水流速的增加则会促进Kaolinite胶体和SiO2胶体的运移。同时还表明,离子强度和流速变化对粒径较大的Kaolinite胶体运移的影响要显著大于SiO2胶体。研究结果有助于加深胶体对污染物运移的促进机制的理解,同时对全面、客观评价地下环境的污染风险具有一定的指导意义。     

柠檬酸对高岭石的溶解作用

采用间歇法(batch method)研究柠檬酸对高岭石溶解的影响。结果表明:低浓度(0.02mmolL-1)柠檬酸可促进高岭石中Ca2+、Mg2+、Na+少量的释放。当柠檬酸浓度分别为1.0mmolL-1和8mmolL-1时,Ca2+,Mg2+,K+,Na+,Si,Al3+阳离子的释放量也相应地增加。释放的Ca2+、Mg2+主要来自高岭石表面的吸附,而Na+、K+则来自高岭石的溶解。     

Fe(Ⅱ)存在条件下氧化铁-高岭石复合物的形成与转化

氧化铁-高岭石复合物是我国南方土壤的重要组分,也是影响这些土壤理化性质的主要因子。本文以Fe(Ⅱ)为添加剂,研究了晶质氧化铁-高岭石复合物的形成与转化过程及其影响因素。结果表明,Fe(Ⅱ)可加速晶质氧化铁-高岭石复合物的形成,在一定程度上克服了高岭石对晶质氧化铁形成的抑制作用。当Fe(Ⅱ)/Fe(Ⅲ)摩尔比(R)在0.04~0.06时,Fe(Ⅱ)可加速纤铁矿、针铁矿、赤铁矿-高岭石复合物的形成;当R≥0.1时,可快速形成磁铁矿-高岭石复合物。在温度50~60℃、pH5~6条件下,Fe(Ⅱ)可加速纤铁矿、针铁矿-高岭石复合物的形成;温度80℃及中性附近时,可加速赤铁矿-高岭石复合物的形成;pH9时,则形成了磁铁矿-高岭石复合物。高岭石的存在减弱了Fe(Ⅱ)对晶质氧化铁形成的催化效果,也可影响产物类型和结晶形貌。上述结果可为自然环境中氧化铁以及氧化铁-高岭石复合物的形成转化过程提供重要参考。     

Longevity of soil water repellency in a former wastewater disposal tree stand and potential amelioration

Previous studies have shown that long-term irrigation with wastewater can lead to the development of soil water repellency. Little is known about the longevity of this effect. Here we address this research gap by examining the effect of long-term (~ 20 years) use of low-quality wastewater for disposal purposes, followed by 6 years of ‘recovery’ with no irrigation, on the wettability of calcareous sandy soil (Xerofluvent) under a Populus alba tree stand used as a “green filter” in SE Spain. Water repellency (WR) and soil organic matter content (SOM) were determined for 120 air-dry samples from the plot and 80 control samples from adjacent and otherwise similar non-irrigated areas. To account for plot micro-topography 40 samples each were taken from ridges (R; 0-5 cm depth), furrows (F; 0-5 cm), and furrows at depth (FD; 5-10 cm). The controls included 40 samples each (0-5 cm depth) from unvegetated and unploughed soil, and from soil under the P. alba plantation.All control samples were non-repellent whereas at the irrigated plot, water repellency was present for 48, 95 and 93% of ridge, furrow and furrow-depth samples respectively. WR and SOM was strongly correlated within the whole sample population (R² = 0.623**) and within two sample groups (R: R² = 0.783**; FD: R² = 0.424**), but weakly within F samples (R² = 0.072 n.s.). The latter showed the highest frequency and persistence (WDPT) of WR, indicating that not only quantity of SOM is controlling WR. Exploratory kaolinite clay additions (0.5-8%) to samples substantially reduced WR even at the lowest concentration, indicating that this could be a promising amelioration treatment for the WR in the soils investigated here.We conclude that for the conditions studied here (i) long-term use with poor-quality wastewater for disposal had led to the development of soil WR, (ii) a 6-year period of ‘recovery’ (i.e. non-irrigation) was insufficient to eliminate the induced WR, and (iii) kaolinite addition could be a promising amelioration treatment for these sandy soils.