On-site remediation of chromium-contaminated sediments by combination of sediment washing and stabilization with magnesium oxide/limestone mixtures

Goal, Scope and Background  The remediation of heavy-metalcontaminated soils and sediments is of significant value to industrial areas around the world. The spread of such pollutants can result in a potential risk of entering the groundwater system and being transported to potential receptors. Leaching techniques can be an effective treatment option for the metal removal from soils and sediments. This approach consists of washing or leaching the contaminated soil with an appropriate reagent and the subsequent treatment of the leaching in an above-ground installation (on-site treatment) where metals can be removed and concentrated into a smaller volume. Among the heavy metals, chromium is a commonly identified soil contaminant, particularly in sites with intensive economic activities including agriculture, industrial, mining and mineral,processing. Objective  The objective of this work was the evaluation and development of a leaching process for the remediation of soils and sediments polluted with chromium at laboratory scale. Chromium soil pollution was generated after the breakdown of a channel containing chromium wastes from a tannery plant. The pollution extension has been estimated to be on the order of thousands of tonnes of soil to be treated, with chromium contents ranging from 500 to 17,000 mg kg^-1 soil. Methods  The whole process investigated in this study integrates three stages; a) chromium leaching from a sediment using a diluted sulphuric acid solution, b) treatment of the leaching effluents with a magnesium oxide/limestone mixture for the precipitation of chromium hydroxide after acidity neutralisation, and c) polishing step to remove the eventual remaining chromium by adsorption onto natural zeolite. The amount of contaminated sediment treated ranged from 0.5 to 2 kg with chromium contents of between 2000 and 17,000 mg kg^-1. Results and Discussion  The paper describes results on the performance of the process and the optimisation of steps including influence of acid sulphuric concentration, chromium removal efficiency as well as alkaline reactive mixture proportions. Effluents from the leaching cells showed a significant decay on the chromium concentration with the increase of leaching runs and a high content of acidity (pH values close to 0.5). The treatment of these effluents in a second cell containing magnesium oxide/ limestone mixtures resulted in a high efficiency in neutralisation of acidity (pH values around 7) and chromium removal (concentrations below 5 mg 1^-1). The passage through a third compartment containing zeolite as an adsorbent decreased the chromium concentration below 0.5 mg 1^-1, Conclusions  From the results obtained on the chromium leaching and immobilisation with magnesium oxide/limestone mixture at a laboratory scale, it could be pointed out that: (a) diluted sulphuric acid solutions (3%) demonstrated a high efficiency on chromium removal from sandy polluted soils on the kilogram scale, (b) mixtures of magnesium oxide/limestone demonstrated a high capacity to neutralise the residual high acidity present on the effluents and to remove chromium by precipitation and (c) between the limestone and caustic magnesia mixtures, those containing more than 60% of caustic magnesia provide the higher efficiency. Recommendation and Outlook  Future work would be directed to the evaluation of the integrated process of leaching and chromium precipitation on column at a scale of 100 to 1000 kg.     

"三岩"造林困难地植被恢复技术研究与示范

湖南造林困难地类总面积达 10 0万hm2 。通过对 5个县 658hm2 试验示范林历时 9年的研究 ,解决了植被恢复技术问题。选出适宜的树、划种有马桑、芦竹、苦槠、牡荆和栓皮栎 5种 ,有发展前景的树种有柏木、铅笔柏和藏柏。选出了林分结构稳定 ,组成种长势好 ,可以肯定的有马桑十墨西哥柏浅层钙质幼年性岩性土等 6个配置模式。并提出和推广了撩壕整地和芦竹下挖上堆 ,施肥促长等造林技术。同时 ,定义了“三岩”造林困难地 ,提出了“三岩”造林困难地的生态环境特点。从土种的水平研究了树种与立地的适应性。     

昆明西山山原红壤和红色石灰土的pH值与磁化率关系研究

通过对昆明西山山原红壤和红色石灰土的pH值和磁化率测试研究发现,山原红壤的pH值在4.0~5.8之间,呈酸性,质量磁化率在56×10-8~174×10-8m3/kg之间,pH值与磁化率呈明显的正相关关系;而红色石灰土pH值在6.0~8.4之间,磁化率为752×10-8~5 056×10-8m3/kg,pH值和磁化率呈负相关关系。该研究表明,在我国西南地区,土壤pH值和磁化率既存在明显的负相关关系也存在正相关关系。结合前人在其他地区的研究资料,进一步发现,土壤的酸碱环境可能是决定这些关系的重要因素。     

广东乳源西京古道植物资源调查及应用

西京古道作为第八批全国重点文物保护单位之一,其历史遗存丰富,且孕育着繁茂的野生植物资源。通过对西京古道的植物资源进行全面的调查,鉴定出维管植物有81科217属266种,其中观赏植物资源68科123属163种(含变种)。通过对西京古道乳源段植物资源的实地调查,掌握了古道沿线植物资源现状并分析其观赏特性及应用价值。在对西京古道沿线植物群落景观进行分析的基础上,提出基于石漠化背景下的古驿道植物景观营造方法及生态修复对策。     

坚持治理开发 山乡面貌大变

坚持治理开发山乡面貌大变柴学松（四川省铜梁县水土保持办公室，６３２５６０）铜梁县双山乡位于涪江支流平滩河的上游，北、西、南三面为坪块低山环绕，中部由七沟八梁的中低丘陵与宽谷构成，在总面积为３３．８３ｋｍ２的范围内，水土流失面积达１３．６４ｋｍ２，森林...     

The effects of crop husbandry and nitrogen fertilizer on nitrate leaching from a shallow limestone soil growing a five course combinable crop rotation

Abstract. Nitrogen (N) leaching losses from a shallow limestone soil growing a five course combinable croprotation (oilseed rape, wheat, peas, wheat, barley) were measured from 1990 until 1995 using porous ceramic cups, at 60 cm depth, and drainage estimates. The crops were grown with three husbandry systems and two levels of N fertilizer. The husbandry systems were designed to reflect local practice (Standard), the best possible techniques to reduce N loss (Protective) and an Intermediate system which was a compromise between the two. Nitrogen was applied at full and half recommended rates. Drainage started during September in four years and November in one year, with above average drainage in three years. Losses of N were largest after peas (58 kg/ha) and oilseed rape (42 kg/ha), and least (17 kg/ha) before peas sown in spring after a cover crop. Over five years, the Protective management system, which used early sowing and shallow cultivation wherever possible, lost least N (31 kg/ha/y) and the Standard system, with conventional drilling dates and ploughing as the primary cultivation, lost most (49 kg/ha/y). Halving the N fertilizer decreased N loss by 11 kg/ha/y, averaged over the rotation. None of the treatments gave mean drainage water nitrate concentrations of less than 50 mg/l, averaged over the five years. Changes to arable cropping alone will not eliminate the need for other measures to control nitrate concen-trations in public drinking water supplies.     

浙江省石灰土光谱特征及其自动识别分类技术研究

本文通过石灰土专题调查，室内土壤光谱测定及其特定及其特征分析，并在此基础上进行土壤光谱自动识别分类方法的对比试验。明确了浙江省石灰土的四个土类，六个土属的光谱特征分异规律；提出了一种参数少，运算量小，精度高的光谱自动识别新方法－分层提取判别法。     

广东石灰岩地区野生观赏植物资源的调查研究

通过对广东省石灰岩地区植物的野外调查，初步发现该地区可作观赏用途的野生植物有４６７种，分隶于１１６科．该地区野生植物资源在生物学特性上有其特殊性，喜钙植物是构成广东石灰岩植被的主要成份．从观赏用途角度出发，该地区观赏植物资源可分为观赏蕨类植物、盆景树桩植物、绿化树种及攀援植物、野生花卉植物、阴生及肉质植物和兰科观赏植物七大类．广东石灰岩观赏植物可分成两个分布区域，即英德至怀集一线以南和以北两个主要分布区．在该线南部地区以常绿植物为主，北部地区有较多的落叶植物；此线以南石灰岩区因植被受破坏严重，种类较贫泛．广东石灰岩地区观赏植物的分布与所处的自然植被带及石灰岩植被的发育和保存状况有密切联系．     

4种灌木林地土壤物理性状及抗侵蚀性能的研究

研究了济南石灰岩山区的黄栌、连翘、绣线菊和黄荆4种灌木林地土壤的物理性状和抗侵蚀性能。结果表明：同一层次不同灌木林地的土壤物理性状存在显著差异，在0～20cm土壤层，黄栌林地的土壤物理性状最好，连翘林地的次之；在20～40cm土壤层．连翘林地的土壤物理性状最好，黄栌林地的次之，黄荆林地和绣线菊林地0～40cm土壤层的物理性状都较差；同一林地0～20cm层的土壤物理性状明显优于20～40cm层;4种灌木林地0～20cm层土壤的有机质含量、水稳性指数和水稳性团聚体含量均大于荒坡地，土壤侵蚀量明显低于荒坡地。     

山东省石灰岩山区灌木林枯落物持水性能的研究

通过对山东省石灰岩山区4种主要灌木林枯落物蓄积量及其持水特性的试验研究,总结出不同林分枯落物的持水性能。结果表明,4种林分枯落物的蓄积量从大到小依次为连翘林>黄栌林>黄荆林>绣线菊林。在前0.5h内,4种林分枯落物吸水速率的大小顺序为绣线菊林>黄栌林>黄荆林>连翘林。4种林分枯落物最大持水量的大小顺序为黄栌林>连翘林>绣线菊林>黄荆林。4种林分枯落物有效拦蓄量的大小顺序为黄栌林>连翘林>绣线菊林>黄荆林。