Evidence for a Neoproterozoic carbonate ramp on the northern edge of the Central African craton: relations with late Proterozoic intracratonic troughs

During Late Proterozoic times, the Archaean Central African craton was affected by trough faulting which led to the formation of grabens, the Sangha aulacogen being the main structure of this type in the studied area. This transverse basin connects with other basins on the northern and south-western borders of the craton. During the Cryogenian, this network of basins was filled with fluvio-deltaic and lacustrine periglacial deposits. The glacio-eustatic transgression in Neoproterozoic III (end-Proterozoic) times flooded extensive areas of shelf on the northern edge of the craton, leading to the development of carbonate sedimentation in a broad outer shelf environment associated with nearshore barriers and evaporitic lagoons. These facies are similar to those developed in the West Congolian Schisto-calcaire (shale-limestone) ramp succession. The North-Central African ramp succession (sediment slope) contains an example of tidal rhythmites in vertical accretion, which occurs beneath the barrier deposits on the subtidal outer shelf. Mathematical analysis of the bedding pattern yields a period of 29–30 days for the lunar month, a result which is in agreement with astrophysical evidence for this epoch (i.e. 650 Ma ago). Major subsidence and seismic activity on this gently sloping platform, associated with the proximity of the Sangha aulacogen, caused the triggering of carbonate turbidites and mass flow deposits. The proliferation of microbial mats under euphotic conditions on an extensive shelf led to the build-up of a carbonate platform. During early Neoproterozoic III times, the West Congolian and North-Central African ramps prograded northwards and southwards, respectively, into the Sangha aulacogen. The sea at that time was restricted to a long graben-like basin, while a remaining area of marine sedimentation persisted into the Palaeozoic. Thus the pattern of end-Proterozoic carbonate sedimentation on the borders of the Central African craton can be interpreted in terms of an overall gently sloping ramp model with progradation converging towards the Sangha aulacogen.     

Vitrification as an alternative to landfilling of tannery sewage sludge

Due to high content of heavy metals such as chromium, tannery sewage sludge is a material which is difficult to be biologically treated as it is in the case of organic waste. Consequently, a common practice in managing tannery sewage sludge is landfilling. This poses a potential threat to both soil and water environments and it additionally generates costs of construction of landfills that meet specific environment protection requirements. Vitrification of this kind of sewage sludge with the addition of mineral wastes can represent an alternative to landfilling.The aim of this study was to investigate the possibility of obtaining an environmentally safe product by means of vitrification of tannery sewage sludge from a flotation wastewater treatment process and chemical precipitation in order to address the upcoming issue of dealing with sewage sludge from the tannery industry which will be prohibited to be landfilled in Poland after 2016. The focus was set on determining mixtures of tannery sewage sludge with additives which would result in the lowest possible heavy metal leaching levels and highest hardness rating of the products obtained from their vitrification.The plasma vitrification process was carried out for mixtures with various amounts of additives depending on the type of sewage sludge used. Only the materials of waste character were used as additives.One finding of the study was an optimum content of mineral additives in vitrified mixture of 30% v/v waste molding sands with 20% v/v carbonate flotation waste from the zinc and lead industry for the formulations with flotation sewage sludge, and 45% v/v and 5% v/v, respectively, for precipitation sewage sludge. These combinations allowed for obtaining products with negligible heavy metal leaching levels and hardness similar to commercial glass, which suggests they could be potentially used as construction aggregate substitutes. Incineration of sewage sludge before the vitrification process lead to increased hardness of the vitrificates and reduced leaching of some heavy metals.     

碳酸盐岩风化形成的土壤剖面上氟的分布及影响因素

选择贵州省新蒲、平坝和罗吏地区的3个碳酸盐岩原地就位风化成土剖面为研究对象,通过对剖面土壤中氟形态、矿物组成、主量地球化学元素和理化性质等的测定实验,讨论了土壤剖面中氟的赋存形态、分布特征及与影响机制。结果表明:罗吏、平坝和新蒲3个剖面残渣态氟含量分别介于896~1 667 mg/kg、897~2 827 mg/kg和1 386~2 852 mg/kg之间,均占各剖面总氟含量的98%以上,3个碳酸盐岩风化形成的土壤剖面中氟主要为残渣结合态;除罗吏剖面外,其它几个剖面吸附性强的无定形铁铝氧化物、结晶态铁铝氧化物与氟含量皆无显著中度以上正相关,有机碳甚至在三个剖面中和氟显著负相关,表明吸附作用对氟富集的贡献有限;次生粘土矿物是氟的主要载体,且主要以残渣态的形式存在于粘土矿物的晶格中,但氟含量与粘粒含量相关性并不显著;采用SPSS软件对氟与各种理化性质进行多元逐步回归分析,回归方程表明镁对氟富集具有重要作用。     

富含黄铁矿的煤矸石中碳酸盐影响其风化淋溶性质的研究

富含黄铁矿的煤矸石在风化淋溶过程中，碳酸盐含量不仅控制其风化程度，而且控制淋溶液的酸度。风化淋溶实验结果表明，Ｆｅ的淋溶量主要受控于酸度，而Ｍｎ＾２＋与ＳＯ４＾２－的淋溶量主要取决于其风化程度。