Copper and antimony extraction from tetrahedrite‐containing dolomite heterotrophic bacteria

Three hundred and thirty‐five strains of heterotrophic bacteria, isolated from various metal‐containing ores, were tested in submerged culture for their capacity to leach copper and antimony from tetrahedrite‐containing dolomitic ore (particle size <0.1 mm; Schwaz, Austria). Experiments showed that after 8 days of incubation, it was possible to differentiate between active and inactive strains. Maximum extraction values for copper (1.0%) and antimony (1.6%) were achieved with Pseudomonas spp. after 8 days. Final pH values were 6.8 in sterile controls and slightly alkaline (up to pH 8.3) in inoculated flasks. Starch and glutamine (C/N ratio of 50:1) proved to be the best carbon and nitrogen sources for growth. Variation of the C/N source resulted in only a very slight increase in the rates of extraction for copper and antimony. Not even 24 h preliminary incubation of a culture before the ore was added improved metal extraction.     

黔东南州白云岩喀斯特区植物群落演化特征

该研究采用时空互代法、连续带指数法等,对贵州省黔东南州的白云岩喀斯特区60个具有代表性的典型样地的植物种组组成、以及各演替阶段植物群落高度、密度、生物量、生物多样性指数、均匀度指数、生态优势度指数等进行调查分析,以探讨白云岩喀斯特区植物群落的演化特征,为深入研究白云岩喀斯特区植物群落自然恢复规律奠定基础。结果表明:(1)各种组的优势种组成不同,种组替代规律依次为先锋种、次先锋种、过渡种,最终被顶极种替代的过程。(2)群落的高度、密度、生物量等结构特征随植物群落演替发展呈逐渐增大趋势,变化范围分别为0.58～9.54m、585～3 145株·hm-2、8.45～128.56t·hm-2。(3)植物群落的物种丰富度随演替阶段的发展呈下降趋势,从草本群落阶段到顶极群落阶段物种数由48种降低到10种。(4)随着植物群落演替阶段的发展,生物多样性指数呈先升高后降低的趋势,即由草本群落的3.48升高到草灌群落的4.73,后降到顶极群落的3.46;均匀度指数呈降低趋势,最高为草本群落阶段的0.95,最低为常绿阔叶林阶段的0.78;生态优势度指数逐渐升高,顶极群落达到最大,为0.10。     

白云岩形成研究的新进展

据统计,全世界50%的碳酸盐岩储层是白云岩,80%以上北美油气碳酸盐岩储存在白云岩中[1-2]。但在现代沉淀环境中几乎找不到原生的白云石踪迹[3],白云石的成因也一直是困扰地质学家们的问题。因此,研究白云石的成因对油气勘探和开发具有战略学意义。近年来,"微生物白云石模型"的提出[4],为解开白云石成因之谜开启了一扇新的窗户。陆续有报道多种微生物的代谢能够介导白云石的形成,但已有研究是在常压下进行,所得到白云石晶体不是天然的菱面型。本期介绍了宋泉颖、张宇等发表的论文"球形赖氨酸芽孢杆菌(Lysinibacillus sphaericus)和嗜冷芽孢八叠球菌(Sporosarcina psychrophila)介导形成白云石晶体"[5],作者首次将压力因素引入白云石成因的研究,并结合微生物菌株的生理特性,综合考察了多重因子对微生物介导形成白云岩的影响,发现球形赖氨酸芽孢杆菌在低温高压微氧条件下,通过尿素水解活性能够介导形成类似于菱面形白云石晶体。该研究是"微生物白云石模型"研究的一个重要进展,也是微生物和地质学交叉研究的一个成功实例。尽管该研究获得了菱面型白云石晶体,但与天然样本尚有差距,分析原因可能是目前的实验条件与自然环境中的白云石形成条件还有所区别,因此,还需要深入地研究才能进一步完善"微生物白云石模型"。     

Removal of Cd2+, Pb2+, and Zn2+ from contaminated water using dolomite powder

Dolomite collected from Surat Thani Province in Thailand was investigated for use as a sorbent for the removal of divalent heavy metal cations from an aqueous solution. The sorbent had a surface area of 2.46 m²/g and a pH of zero point charge (pHzpc) of 9.2. Batch sorption was used to examine the effect of the pH (pH 3–7) on the sorption capacity of Cd²⁺, Pb²⁺ and Zn²⁺, alone or together as an equimolar mixture at various concentrations. Alone, each heavy metal cation was adsorbed faster at a higher pH, where the sorption of Cd²⁺ and Pb²⁺ fitted a Langmuir isotherm, but Zn²⁺ sorption best fitted a Freundlich isotherm. Under equimolar competitive sorption, the sorption capacity of each cation was decreased by 75.8% (0.29–0.07 mM/g), 82.8% (0.53–0.09 mM/g), and 95.7% (0.84–0.04 mM/g) for Cd²⁺, Pb²⁺ and Zn²⁺, respectively, compared to that with the respective single cation. Desorption of these heavy metal cations from dolomite was low, with an average desorption level of 0.06–17.4%. Furthermore, since dolomite is readily available and rather cheap, it is potentially suitable for use as an efficient sorbent to sorb Cd²⁺ and Pb²⁺, and perhaps Zn²⁺, from contaminated water.     

Microbial influence on dolomite and authigenic clay mineralisation in dolocrete profiles of NW Australia

Dolomite (CaMg(CO₃)₂) precipitation is kinetically inhibited at surface temperatures and pressures. Experimental studies have demonstrated that microbial extracellular polymeric substances (EPS) as well as certain clay minerals may catalyse dolomite precipitation. However, the combined association of EPS with clay minerals and dolomite and their occurrence in the natural environment are not well documented. We investigated the mineral and textural associations within groundwater dolocrete profiles from arid northwest Australia. Microbial EPS is a site of nucleation for both dolomite and authigenic clay minerals in this Late Miocene to Pliocene dolocrete. Dolomite crystals are commonly encased in EPS alveolar structures, which have been mineralised by various clay minerals, including montmorillonite, trioctahedral smectite and palygorskite-sepiolite. Observations of microbial microstructures and their association with minerals resemble textures documented in various lacustrine and marine microbialites, indicating that similar mineralisation processes may have occurred to form these dolocretes. EPS may attract and bind cations that concentrate to form the initial particles for mineral nucleation. The dolomite developed as nanocrystals, likely via a disordered precursor, which coalesced to form larger micritic crystal aggregates and rhombic crystals. Spheroidal dolomite textures, commonly with hollow cores, are also present and may reflect the mineralisation of a biofilm surrounding coccoid bacterial cells. Dolomite formation within an Mg-clay matrix is also observed, more commonly within a shallow pedogenic horizon. The ability of the negatively charged surfaces of clay and EPS to bind and dewater Mg²⁺, as well as the slow diffusion of ions through a viscous clay or EPS matrix, may promote the incorporation of Mg²⁺ into the mineral and overcome the kinetic effects to allow disordered dolomite nucleation and its later growth. The results of this study show that the precipitation of clay and carbonate minerals in alkaline environments may be closely associated and can develop from the same initial amorphous Ca–Mg–Si-rich matrix within EPS. The abundance of EPS preserved within the profiles is evidence of past microbial activity. Local fluctuations in chemistry, such as small increases in alkalinity, associated with the degradation of EPS or microbial activity, were likely important for both clay and dolomite formation. Groundwater environments may be important and hitherto understudied settings for microbially influenced mineralisation and for low-temperature dolomite precipitation.     

Passive Treatment of Mn-Rich Mine Water: Using Fluorescence to Observe Microbiological Activity

Abstract

Conventionally, limestones have been used in passive mine water treatment systems. Limestones with the highest proportion of calcite are recommended since they have the greatest long-term alkalinity generating potential. Manganese is present in mine waters and needs to be removed in order to comply with environmental quality standards. This paper compares seven different Permian carbonate rocks, both limestone and dolomite, in their ability to promote manganese oxidation in real mine waters over an 8-h period. The substrates are characterised using thermogravimetric analysis, X-Ray diffraction and scanning electron microscopy. Fluorescence spectrophotometry is used to monitor any changes in the dissolved organic matter concentration in the water as manganese is removed. We determine that there is no statistically significant correlation between manganese removal and the proportion of calcite or between manganese removal and substrate surface roughness. Fluorescence spectrophotometry demonstrates that there is a distinct change in the observed spectra in the water during manganese removal. There is a positive and statistically significant correlation between manganese removal and the production of a tyrosine-like substance (up to ～150 ppb in 8 h), which fluoresces at 270–280 nm excitation wavelength and 300–310 nm emission wavelength, suggesting that microbial activity is an important factor in promoting manganese removal within dolomite passive treatment systems. It may be possible to use fluorescence spectrophotometry to monitor for microbial activity in passive treatment systems.