Modified column flotation of adsorbing iron hydroxide colloidal precipitates

A promising technique for the removal of heavy metal ions from wastewater streams involved firstly the ions adsorption on a colloidal precipitate (carrier) and then the separation of the loaded flocs (coagula) by a modified column flotation. Here, the effluent feed and the carrier (ferric hydroxide) enter smoothly by the top of the column through a special diffuser, in counter current with rising bubbles (100–600 μm diameter) generated by using recycled water, surfactant and air suction through a venturi. High separation values of the column flotation of the carrier precipitates were achieved, despite the high superficial flow rate and the high Fe^+ 3 concentration utilized (> 60 mg L^− 1 Fe). No rupture of colloidal carrier aggregates was observed and a low split was ensured by monitoring the concentrate (floated product) flow rate. Results indicated that best separation was attained by controlling the medium pH (for best heavy metal ion adsorption onto the carrier), followed by sodium oleate, used as “collector” and optimizing operating parameters (conditioning, flow rates, etc.). The column throughput reached 43 m h^− 1 (m³ m^− 2 h^− 1), which is about 4 times the normal capacity of DAF-dissolved air flotation unit, the most used floater in wastewater treatment. Various metals (Cu, Ni, Pb, etc.) and molybdate ions present in synthetic and real effluent were successfully removed based on this colloidal adsorbing flotation principle. The process was also applied in a pilot scale to treat an industrial electroplating wastewater. Most of toxic metals (Cu, Ni and Zn) were reduced from initial concentrations of about of 2 to 10 mg L^− 1, to below 0.5 to 1.0 mg L^− 1, meeting local municipal discharge limits (but Cd ions). It is believed that flotation separation using medium-sized bubbles has great potential as a clean water and wastewater treatment technology.     

Visualization experiments of iron precipitates: Application for in-situ arsenic remediation

Laboratory experiments were carried out to acquire more insight and understanding of the phenomena associated with the in-situ arsenic remediation. Visualization techniques are the most informative for the detection of Fe(II) while flowing in soils. Green Rust (GR) was considered as representative of in-situ iron precipitates. In a visualization flat cell, the change in color of GR to orange, due to oxidation, was monitored by a digital camera and the images were analyzed giving the spatial and temporal distribution of Fe(II). Moreover, both oxygen and pH changes in time were recorded in two sections along the flow direction in the cell. The measured and calculated concentration profiles were compared and the actual reaction rates were predicted. The reaction rate constants measured in this study, under flowing conditions, are in a good agreement with the values obtained from batch experiments reported in the literature.     

硅藻土、石英砂和钾离子促进微生物转化酸性矿山废水中亚铁成次生矿物的研究

嗜酸性氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)能够在低pH值条件下,迅速将Fe2+氧化并产生大量次生羟基硫酸铁沉淀,从而除去水中可溶性Fe2+。这为富含Fe2+的酸性矿山废水(acid mine drainage,AMD)处理提供了新的思路。本文从晶种刺激和阳离子诱导两个方面,分别研究了固定化载体(硅藻土、石英砂)和具有强诱导能力的成矾离子(K+)对微生物转化酸性体系中Fe2+成次生矿物的影响。结果表明,3种材料均有明显促进可溶性Fe2+向次生矿物转化的作用,且总铁(TFe)沉淀率与3种材料的添加量呈正相关关系。在起始Fe2+浓度为160mmol/L,硅藻土、石英砂和钾离子最大添加量分别为10 g、10 g和80 mmol/L时,经过72 h反应后,TFe沉淀率分别比对照增加了8%、24%和20%。矿物中的Fe、K和S元素含量与溶液中的起始K+浓度有非常密切的关系,随着K+浓度的增大,矿物中的K和S含量逐渐增加,而Fe含量则相应减少。     

Biomimetic phosphoryl transfer catalysed by iron(II)-mineral precipitates

Iron(II) minerals have been found to catalyse the formation of pyrophosphate from activated phosphate compounds and inorganic phosphate at near neutral pH in water. Iron(II) phosphate catalyses the formation of pyrophosphate, from either acetyl phosphate or phosphoenolpyruvate as the activated phosphoryl donor, in yields of up to 25% and 14% respectively. Under similar conditions, these minerals also retard the hydrolysis of pyrophosphate. The catalysis of pyrophosphate formation is tolerant of sulfide ions: pyrophosphate being produced from acetyl phosphate in 12% yield in the presence of equimolar amounts of sulfide. These reactions mimic the extant biosynthesis of ATP from acetyl phosphate or phosphoenolpyruvate; they counter the concern that hydrolysis of polyphosphates would out-compete their accumulation under prebiotic conditions; and hence suggest a possible prebiotic route to polyphosphates under conditions that may have occurred on the early earth.     

The mechanism of iron removal in estuaries

A survey of U.S. east coast estuaries confirms that large-scale rapid removal of iron from river water is a general phenomenon during estuarine mixing. The river-borne ‘dissolved’ iron consists almost entirely of mixed iron oxide-organic matter colloids, of diameter less than 0.45 μm, stabilized by the dissolved organic matter. Precipitation occurs on mixing because the seawater cations neutralize the negatively charged iron-bearing colloids allowing flocculation. The process has been duplicated in laboratory experiments using both natural filtered and unfiltered river water and a synthetic colloidal goethite in 0.05 μm filtered water. The colloidal nature of the iron has been further confirmed by ultracentrifugation and ultrafiltration. A major consequence of the precipitation phenomena is to reduce the effective input of ‘dissolved’ iron to the ocean by about 90% of the primary river value, equivalent to a concentration of less than 1 μmol per liter of river water.     

Characterization of manganese oxide precipitates from Appalachian coal mine drainage treatment systems

The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnO_x). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20–150 mg/L), system construction (±inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 °C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnO_x precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnO_x precipitates from all sites was coarse and “sponge-like” composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnO_x precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnO_x mineral assemblages in CMD treatment systems.     

Kinetics of removal of iron colloids from estuaries

Laboratory experiments indicate that colloidal Fe is aggregated in estuarine waters by a second-order kinetic mechanism. The corresponding rate coefficient is proportional to the square of the salinity. A simple theoretical formulation is presented to describe the distribution of Fe in an estuary, based on observed second-order kinetics. The distribution depends on a single parameter whose value may be determined from measurements of the physical characteristics of the estuary. The theoretical expression accurately predicts observed distributions of Fe in a variety of estuaries, suggesting general applicability.     

Simulation of an in situ iron removal test

This article outlines the main mechanisms for in-situ removal of iron from groundwater. The dependence of ferrous iron kinetic oxidation by dissolved oxygen on the temperature and pH in bicarbonate near neutral groundwater was investigated. The dependence of oxygen consumption efficiency on the iron sorption coefficient, pH, and temperature of groundwater was obtained as a result of modeling of the one well in-situ iron removal test in the Amurskiy water intake facilities.     

Efficiency of 2D CDP during section subsurface investigations

Today, all seismic onshore and offshore oil and gas explorations are performed using the common depth point (CDP) method. However, the standard methods of data acquisition and processing often turn out to be inefficient for shallow seismic purposes. We made an attempt to estimate CDP efficiency by solving the direct problem using ray-path modeling under varying model parameters.     

Extensive degradation and fractionation of organic matter during subsurface weathering

Organic carbon, sulphur, ¹³C_org, iron, manganese and calcium have been measured across a subsurface-weathering front in Pliocene sediments in southern Sicily. The results show an almost quantitative removal of C_org and sulphur and an increase in iron and manganese oxides over the weathering front, accompanied with a significant shift of the ¹³C_org to lower values. These data are among the first to support the rapid, extensive weathering of sedimentary organic matter and sulphur, a basic assumption made in global biogeochemical models on a Phanerozoic timescale.     

碱熔除铁氟化物置换容量法测定铁矿石中的三氧化二铝

试样经氢氧化钠碱熔,过滤分离铁等元素,将滤液酸化、DETA络合、氟化钠置换,再用硫酸铜标准溶液回滴释放出来的EDTA,从而实现对铝的测定,通过本方法对铁矿石标准物质及样品的测定,结果的相对标准偏差在0.93%~2.95%之间,且铁矿石标准物质测定值与认定值相符。     

Characterization of subsurface geometry and radioactivity distribution in the trench containing Chernobyl clean-up wastes

Several radiometric and geophysical methods were applied to characterize the subsurface geometry and radioactivity distribution (especially ¹³⁷Cs) in a trench with low-level wastes at the Chernobyl site. While surface dose rate measurements and electromagnetic soil conductivity survey produced uninterpretable fields of signals, the ground penetrating radar appeared to be an efficient method for characterization of the subsurface geometry of the waste burial. It was established that the trench had the following dimensions: the length was 70 m; average width 6–8 m, and depth 2–2.5 m. Data on ¹³⁷Cs distribution in the trench were obtained by means of a borehole gamma-logging technique. The total inventory of ¹³⁷Cs was estimated at 600±200 GBq. Geostatistical analysis using the semivariogram function has shown regular spatial correlation patterns for the logarithm-transformed ¹³⁷Cs activity of waste material. The correlation length along the trench was 17 m, while across the trench, and in the vertical direction, it was 4 m. The observed correlation patterns supposedly were caused by the method used to dispose the contaminated topsoil: the bulldozing in the direction perpendicular to a trench axis. Obtained results may be useful for selecting a characterization method and for optimization of sampling strategies for similar waste sites.     

Evaluation of mineral substrates for in situ iron removal from groundwater

Calcium carbonate-based materials (CCBM) have been found to remove Fe(II) and other divalent metal cations from aqueous solution and thus have the potential for incorporation into remediation systems to remove Fe(II) from groundwater at landfills. Research was conducted to examine the ability of a range of CCBM to remove Fe(II) and assess the mechanism of removal. Different CCBM (limestone, concrete, dolomite, marble), as well as gypsum, witherite, and quartz sand, were tested for their ability to remove Fe(II) from water using batch tests conducted under anaerobic conditions. Limestone (specific surface area of approximately 0.46 m²/g) was found to have the best removal effectiveness, and the final Fe(II) concentration was reduced from 50 to <0.01 mg/L. Kinetics experiments conducted over a 72 h period indicated that the removal process of Fe(II) by CCBM was a two-step process. The first step is rapid sorption of Fe(II) onto the CCBM surfaces within the first hour, and the second step is relatively slow co-precipitation of iron-containing solids formed through various chemical reactions. The two best performing CCBM (limestone and concrete) were evaluated for their removal ability based on media particle size (diameters of 3–5, 7–10, 15–25, and 40–50 mm) and revealed statistically significant (p < 0.01) increases in Fe(II) removal for each particle size class examined. SEM analysis of reacted materials revealed visible precipitates on the reactive material surface; XRD analysis was not able to detect crystalline Fe minerals on limestone surface.     

钾长石粉酸浸除铁的实验研究

在利用钾长石粉合成沸石分子筛和制取碳酸钾技术中，铁的存在会降低沸石的白度。对北京平谷、天津蓟县、内蒙白云鄂博三地钾长石粉进行硫酸酸浸除铁实验，获得最大铁浸出率分别为88．6％、93．2％和64．6％，且前两地钾长石粉中铁的浸出行为相似，酸浸除铁效果均优于白云鄂博钾长石粉。采用正交实验法研究硫酸浓度、酸浸温度和时间对除铁效果的影响，表明三者对不同地区钾长石粉酸浸除铁效果的影响程度各不相同。钾长石酸浸除铁反应开始时，铁的溶解极快，反应速率主要由化学反应控制；其后溶解相对缓慢，反应速率则由扩散作用控制。     

蛇纹石化过程中铁活动性的高温高压实验研究

蛇纹石化过程中铁的活动性影响铁氧化物的形成和体系的氧逸度。然而,关于橄榄岩蛇纹石化过程中各矿物(橄榄石、斜方辉石和单斜辉石)蚀变过程中铁的活动性仍没有详细的研究。本文报道了80~200℃、饱和蒸气压下,不同的初始流体、水岩比条件下,橄榄岩蛇纹石化过程中铁的活动性。结果表明,蛇纹石化流体的铁含量较低(0.0~0.7mmol/kg),没有形成铁氧化物或铁氢氧化物,铁主要富集在蛇纹石和未反应的初始矿物中(例如,橄榄石和辉石)。由橄榄石蚀变形成的蛇纹石和由斜方辉石蚀变生成的蛇纹石化学组成相差较大,前者富铁而贫铝,后者贫铁而富铝。但当初始流体为碱性的0.5mol/L Na Cl(aq)时,两种不同来源的蛇纹石组成相差不大。尤为重要的是,单斜辉石蚀变生成的蛇纹石铁含量较高,8.1%~10.2%Fe O,远高于单斜辉石的铁含量(2.6%Fe O)。以上表明,低温蛇纹石化过程中,铁不能够大规模、长距离的运移,但在微米尺度上是活动的。     

Characterization of the subsurface urban heat island and its sources in the Milan city area,Italy

Urban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and?+?0.4 °C/year that leads to a gain of 25 MJ/m² of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.

     

Prior model identification during subsurface flow data integration with adaptive sparse representation techniques

Construction of predictive reservoir models invariably involves interpretation and interpolation between limited available data and adoption of imperfect modeling assumptions that introduce significant subjectivity and uncertainty into the modeling process. In particular, uncertainty in the geologic continuity model can significantly degrade the quality of fluid displacement patterns and predictive modeling outcomes. Here, we address a standing challenge in flow model calibration under uncertainty in geologic continuity by developing an adaptive sparse representation formulation for prior model identification (PMI) during model calibration. We develop a flow-data-driven sparsity-promoting inversion to discriminate against distinct prior geologic continuity models (e.g., variograms). Realizations of reservoir properties from each geologic continuity model are used to generate sparse geologic dictionaries that compactly represent models from each respective prior. For inversion initially the same number of elements from each prior dictionary is used to construct a diverse geologic dictionary that reflects a wide range of variability and uncertainty in the prior continuity. The inversion is formulated as a sparse reconstruction problem that inverts the flow data to identify and linearly combine the relevant elements from the large and diverse set of geologic dictionary elements to reconstruct the solution. We develop an adaptive sparse reconstruction algorithm in which, at every iteration, the contribution of each dictionary to the solution is monitored to replace irrelevant (insignificant) elements with more geologically relevant (significant) elements to improve the solution quality. Several numerical examples are used to illustrate the effectiveness of the proposed approach for identification of geologic continuity in practical model calibration problems where the uncertainty in the prior geologic continuity model can lead to biased inversion results and prediction.