废物水泥窑共处置产品中Cd释放的pH影响

用高温电炉模拟煅烧试验制取水泥熟料后再制作混凝土,参考EA NEN 7375:2004浸出试验,设定5种不同pH的浸取液对混凝土进行长期浸出试验,研究了pH对水泥窑共处置混凝土中Cd释放量以及释放过程的影响.结果表明:(1)pH为2.00、3.50、5.00、7.35和10.00的浸取液中,Cd的累积释放量分别为0.408 0、0.005 8、0.000 7、0.000 4、0.001 2 mg/kg.在酸性条件下,随pH的增大,Cd的累积释放量减小.在碱性条件下,随pH的增大,Cd的累积释放量增大.(2)pH为7.35的浸取液中,Cd累积释放量的释放曲线与斜率为0.5的直线拟合最佳.pH为7.35的浸取液中,混凝土中Cd的释放机制为扩散控制;pH为2.00和5.00的浸取液中,Cd的释放在前期为扩散控制,后期发生了耗竭作用;pH为3.50和10.00条件下,Cd的释放在前期发生了延滞作用,中期为扩散控制,后期发生了耗竭作用.     

间歇浸取对废物水泥窑共处置产品中Cr和As释放的影响

研究间歇浸取条件下废物水泥窑共处置产品中重金属Cr、As的释放,对水泥产品在实际应用中的环境安全性评价有重要意义.通过模拟煅烧实验制取含Cr和As的水泥熟料,并制取混凝土样品,采用pH影响实验和扩散浸出实验,研究了混凝土中Cr和As的溶解特性及其间歇浸取对混凝土中Cr和As释放的影响.结果表明,浸取方式对浸取液pH有较...     

废物水泥窑共处置产品中重金属释放模型研究——混凝土路面场景

通过模拟煅烧试验制取水泥熟料,并制得混凝土样品。在混凝土路面场景分析的基础上,参照欧盟固体中无机组分有效量测试方法(EA NEN7371),以pH=3.2的HNO3/H2SO4溶液(质量比为1∶2)为浸取液,在液固比为20 L/kg条件下,对混凝土样品进行模拟浸出实验;参照欧盟块状材料中无机组分的扩散实验方法(EA NEN7375)测定混凝土样品中重金属的有效释放量。模拟浸出实验结果表明,Cr、Ni和Cd在浸出过程中扩散控制是其释放的主要因素。在此基础上建立了重金属在混凝土路面中的释放模型。实验室实测累积释放量(实测值)与模型预测累积释放量(预测值)的拟合检验结果表明,实测值与预测值之间差异不显著,释放模型能较好地预测混凝土路面中重金属的长期累积释放量。     

液固比对含重金属水泥熟料制品中重金属释放的影响

通过模拟煅烧试验制取水泥熟料,参照JGJ 55-2000（《普通混凝土配比设计规程》）制取混凝土样品,参考SR003.1和NEN 7375浸出试验,分别研究液固比对粒状及块状混凝土样品中重金属（Cr、Ni和As）释放的影响。结果表明,在不同液固比条件下粒状混凝土中的重金属浸出浓度为Cr>Ni>As,Cr、As浸出浓度基本保持不变,分别为2 500 μg/L左右和5～6 μg/L,Ni在液固比（L∶S）<6时,浸出浓度随着液固比的增加而降低,在L∶S>6时,浸出浓度较稳定,为35.7～41.5 μg/L;浸出量均随着液固比的增加而增大。液固比（L∶S）<10时,块状混凝土中重金属累积释放量及扩散系数均随液固比的增加而增大,当L∶S>10时两者基本保持不变。     

硫酸钛混凝去除无机砷(Ⅲ)的效能

使用硫酸钛作为混凝剂,研究了混凝去除As(Ⅲ)过程中溶液pH值、混凝剂投加量、砷的初始浓度以及阴离子对除砷效果的影响.硫酸钛的水解沉淀物颗粒等电点为pH =5;当pH =6时,水解沉淀物的粒径最大.在pH =5 ～8范围内,As(Ⅲ)的去除率高且基本稳定;而沉淀物颗粒Zeta电位降低较大.说明水解沉淀物Zeta电位对As(Ⅲ)的去除影响不大.混凝剂投加量为2.5 ～10 mg/L时,As (Ⅲ)的去除率随投加量的增加而显著增加;混凝剂投加量大于15 mg/L时,As(Ⅲ)去除率随混凝剂投加量的增加变化趋于平缓.水中阴离子(硅酸根和磷酸根离子)的存在会降低混凝对As (Ⅲ)的去除效率.     

铅冶炼水淬渣中金属源释放特征及影响因素

固废中金属源释放机理和特征研究对于环境管理和环境风险防控具有重要意义。采用连续浸出和渗流释放方法,分析了铅冶炼水淬渣中金属元素在不同pH、液固比以及溶解性有机质(DOM)条件下的释放特征。结果表明,铅冶炼水淬渣中含有Cr、Co、Cd、Ni、Mo、Zn等重金属,Al、Li含量也较高。液固比影响金属释放率,总体上液固比越大释放率越大。金属种类和释放率受pH影响显著,在pH=4.5时有Cd、Zn、Mo和Ni溶出;而在pH=7.0时只有Mo溶出,累积释放率也低于pH=4.5时。在相同pH下DOM促进了Mo释放。在实际场景中,应加强含金属类固废全生命周期的风险管控。     

模拟酸雨对土壤中的铜释放与缓冲作用研究

研究了模拟酸雨淋溶过程中对南方主要土壤重金属Cu的缓冲及释放现象。结果表明，土壤的Cu释放量随淋溶模拟酸雨pH值的下降而增大，酸雨的pH值是影响土壤重金属离子释放和迁移的主要因素，当pH〈3．0时，Cu的释放量明显增加，并且增长迅速。此外，淋溶量也是影响土壤中Cu释放的重要因素。     

pH值对烧结砖中重金属释放的影响

采用酸消解实验和NEN 7371浸出实验研究了烧结砖中重金属总量和有效释放量,采用pH-dependence实验研究pH对破碎烧结砖样品中重金属(Cr、Ni、As、Cd和Pb)浸出特性的影响,以及烧结砖样品的酸碱缓冲容量。结果表明,烧结砖中重金属的有效释放量低于总量,释放率从大到小依次为CdAsPbNiCr;烧结砖的酸缓冲容量较小,浸出液pH从7.03降到3.64,消耗了29.33 mmol/kg硝酸,碱缓冲容量较大,pH从7.03升到12.40,共消耗256 mmol/kg氢氧化钠溶液,因此在使用烧结砖的过程中要特别注意环境pH;浸提液的酸碱性是影响烧结砖中重金属浸出的重要参数,在实验研究的pH范围内,不同重金属的浸出规律不同。Cr和As的释放受pH影响较小,而Ni和Cd的浸出量随pH的增大而降低,Pb的浸出量在强酸和强碱条件下均较大,当pH在5.59~9.86的范围内浸出量很低。     

pH对δ-MnO_2和水铁矿吸附As(Ⅴ)的影响

研究了初始pH对δ-MnO_2和水铁矿吸附As(Ⅴ)的动力学和热力学过程的影响。结果表明,不同初始pH对水铁矿去除As(Ⅴ)的效果影响不明显,而对δ-MnO_2去除As(Ⅴ)的效果影响较大。在相同的吸附时间下,初始pH=5.0时,As(Ⅴ)去除率最高,且随初始pH增大而降低。当初始pH=5.0时,δ-MnO_2和水铁矿对As(Ⅴ)的平衡吸附量总体上都大于初始pH=7.0或初始pH=9.0时。准二级动力学方程可以很好地描述δ-MnO_2和水铁矿吸附As(Ⅴ)的动力学过程。Freundlich方程拟合水铁矿和δ-MnO_2吸附As(Ⅴ)的过程优于Langmuir方程。     

四平市二龙湖底泥磷释放研究

采用室内实验模拟法对四平市二龙湖富营养化限制因子磷的底泥释放速率及释放量进行了研究,并研究在各种环境因子（温度、pH、DO和扰动因素）影响下底泥磷的释放规律.结果表明,（1）二龙湖年平均底泥释磷量为208.78kg,最大释磷率为0.889 μg/g（T=20℃,pH=8,DO为4.68 mg/L）;（2）自然和人为的扰动因素会促进底泥的磷释放;（3）pH在弱酸至中性范围内底泥释磷量最小,酸性和碱性条件都有利于磷的释放;（4）随着温度的升高底泥释磷量增大;（5）厌氧条件比好氧条件更有利于磷的释放.     

Arsenic release from iron rich mineral processing waste: Influence of pH and redox potential

This paper presents the effect of pH and redox potential on the potential mobility of arsenic (As) from a contaminated mineral processing waste. The selected waste contained about 0.47 g kg(-1) of As and 66.2 g kg(-1) of iron (Fe). The characteristic of the waste was identified by acid digestion, X-ray diffraction and sequential extraction procedures. Less than 2% of the total As was acid extractable with the remaining 98% associated with Fe-oxyhydroxides and oxides. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. Arsenic leaching followed a "V" shaped profiles with significant leaching in the acidic and alkaline pH region. Acid extractable phases dissolved at acidic pH, while desorption of arsenic due to increase in pH resulted in high arsenic concentration at alkaline pH. Under aerobic conditions and pH 7, As solubility was low, probably due to its precipitation on Fe-oxyhydroxides. Maximum As solubilization occurred at pH 11 (3.59 mg l(-1)). Similarity in the As and Fe leaching profiles suggested that the release of As was related to the dissolution of Fe in the low pH region. In general, redox potential did not play a significant role in arsenic or iron solubilization. It was thus concluded that for this solid waste, desorption was the predominant mechanism in arsenic leaching. A simple thermodynamic model based on arsenic and iron redox reactions was developed to identify the more sensitive redox couple.     

Source and release mechanism of arsenic in aquifers of the Mekong Delta, Vietnam

In order to elucidate the arsenic source and its release mechanism into groundwater in the Mekong Delta, Vietnam, groundwater samples were collected from wells at different depths (20 to 440 m) and core samples (from 20 to 265 m depth) were analyzed. Based on the analytical results for groundwater and core samples, the As source in groundwater is considered to be pyrite (FeS(2)) in acid sulfate soil (ASS) under oxidizing conditions and hydrous ferric oxide (Fe(OH)(3)) under reducing conditions. Geochemical modeling demonstrated that As(III) is the dominant species and the presence of As-bearing sulfides, Fe-bearing sulfides and oxides phases may locally act as potential sinks for As. From variation between Fe and As concentrations in groundwater samples, the release mechanism of As is: dissolution of Fe(OH)(3) containing As under reducing conditions and oxidative decomposition of FeS(2) containing As under oxidizing conditions.     

Prediction of adsorption rate of phosphate removal from wastewater with gas concrete

Gas concrete, a conventional structural material, is used to remove phosphate from wastewater. A batch study of phosphate removal from wastewater with waste particles of gas concrete has been performed. The concentration-time graphs were plotted against pH, temperature, and agitation speed, and the reaction rate equation was adapted to adsorption. The differential method was used to define reaction rate. The adsorption rates, reaction rate constants, and reaction rates were determined by tangent lines of drawn curves at different concentrations, depending on pH, temperature, and agitation speed. The adsorption rate increased with pH and temperature. The maximum effect of agitation speed on the adsorption rate was observed at 150 rpm. The activation energy of reaction and the pre-exponential factor were calculated using the Arrhenius equilibrium equation. The zeta potentials of waste gas concrete were determined at various pH values. The surface area of gas concrete was obtained using BET apparatus as 22 m2/g. The composition of gas concrete was determined by X-ray diffractometry. The results indicate that gas concrete is an effective adsorbent to remove phosphate from wastewater.     

Effects of bacterial activities on the release of heavy metals from contaminated dredged sediments

The potential impact of indigenous bacterial processes on the release of heavy metals from dredged sediment deposits was investigated. Batch re-suspension experiments were conducted in order to investigate the release of Zn, Cd, Cu and Pb from a polluted anoxic sediment submitted to oxidative perturbations. The concentrations of heavy metals, sulphate and dissolved organic carbon (DOC) were periodically recorded, and cell counts were performed to follow the evolution of several bacterial species. The specific effects of microbial processes were quantified by performing re-suspension assays on sterilised samples. Moreover, the effect of an initial acidification of the system was studied. The results showed that metal release was mainly due to oxidation of sulphide minerals contained in the sediment. Sulphur-oxidising bacteria such as Acidithiobacillus thiooxidans were identified to play a major role in the process, by enhancing the oxidation kinetic. However, the acid production resulting from these reactions was almost totally buffered by the dissolution of the calcite present in the sediment. Copper was released to a lesser extent, and a strong association with organic matter was observed. Lead was not observed in solution, because of its low solubility at neutral conditions and of its re-adsorption on the solid phase. The initial acidification of the system resulted in an faster growth of the acidophilic A. thiooxidans. A subsequent pH drop originating from microbial processes was then observed during the first stages of the experiment. As a consequence, drastic increases in metal (Zn, Cd) release were observed.     

Kinetics of metribuzin release from bentonite-polymer composites in water

A series of bentonite polymer-composites (BPCs) loaded with metribuzin were studied for their controlled release in aqueous medium. The release of active ingredient from BPCs was significantly lower as compared to commercial metribuzin formulation. The results revealed that the cumulative metribuzin release was highest (81%) from the BPCs containing 8% clay (commercial bentonite) and 2% metribuzin which correspond to the lowest (14 days) half-life values i.e., time required for 50% release of active ingredient (t_1/2). The metribuzin release from the BPCs decreased with increased concentration of clays in polymer matrix and the release was further decreased with BPCs prepared with pure nano-bentonite. BPCs containing 12% clay and 2% metribuzin showed maximum t_1/2 values i.e., 25 and 51 days for commercial bentonite and pure nano-bentonite as clay sources, respectively. The differential behaviour in the metribuzin release rates from BPCs was ascribed due to variations in crosslinking of metribuzin in the composites. As metribuzin release was found to be slower in BPCs compared to commercial formulation, it could be used for control of weeds tailored to different crops.     

Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin

An adsorption process for the removal of As(V) and As(III) was evaluated under various conditions using zirconium(IV) loaded chelating resin (Zr-LDA) with lysine-Nalpha,Nalpha diacetic acid functional groups. Arsenate ions strongly adsorbed in the pH range from 2 to 5, while arsenite was adsorbed between pH 7 and 10.5. The sorption mechanism is an additional complexation between arsenate or arsenite and Zr complex of LDA. Adsorption isotherm data could be well interpreted by Langmuir equation for As(V) at pH 4 and As(III) at pH 9 with a binding constant 227.93 and 270.47 dm3 mol(-1) and capacity constant 0.656 and 1.1843 mmol g(-1), respectively. Regeneration of the resin was carried out for As(V) using 1 M NaOH. Six adsorption/desorption cycles were performed without significant decrease in the uptake performance. Column adsorption studies showed that the adsorption of As(V) is more favorable compared to As(III), due to the faster kinetics of As(V) compared to As(III). Influence of the coexisting ions on the adsorption of As(V) and As(III) was studied. The applicability of the method for practical water samples was studied.     

Desorption of cadmium from goethite: effects of pH, temperature and aging

Cadmium is perhaps environmentally the most significant heavy metal in soils. Bioavailability, remobilization and fate of Cd entering in soils are usually controlled by adsorption-desorption reactions on Fe oxides. Adsorption of Cd on soil colloids including Fe oxides has been extensively studied but Cd desorption from such soil minerals has received relatively little attention. Some factors that affect Cd adsorption on goethite include pH, temperature, aging, type of index cations, Cd concentrations, solution ionic strength and presence of organic and inorganic ions. This research was conducted to study the influence of pH, temperature and aging on Cd desorption from goethite. Batch experiments were conducted to evaluate Cd desorption from goethite with 0.01 M Ca(NO3)2. In these experiments Cd desorption was observed at 20, 40 and 70 degrees C in combination with aging for 16 h, 30, 90 and 180 d from goethite that adsorbed Cd from solutions containing initial Cd concentrations of 20, 80 and 180 microM. Following the adsorption step Cd desorption was measured by 15 successive desorptions after aging at various temperatures. At the lowest amount of initially adsorbed Cd and equilibrium pH 5.5, cumulative Cd desorption decreased from 71% to 17% with aging from 16 h to 180 d and the corresponding decrease at equilibrium pH 6.0 was from 32% to 3%. There was a substantial decrease in Cd desorption with increasing equilibration temperature. For example, in goethite with the lowest amount of initial adsorption at equilibrium pH 5.5, cumulative Cd desorption decreased from 71% to 31% with increase in temperature from 20 to 70 degrees C, even after 16 h. Dissolution of Cd adsorbed goethite in 1M HCl, after 15 successive desorptions with 0.01 M Ca(NO3)2, indicated that approximately 60% of the Cd was surface adsorbed. Overall, dissolution kinetics data revealed that 23% to 88% Cd could not be desorbed, which could possibly be diffused into the cracks and got entrapped in goethite crystals. At elevated temperature increased equilibrium solution pH favoured the formation of CaCO3 and CdCO3 which reasonably decreased Cd desorption. Cadmium speciation showed the formation of calcite and otavite minerals at 40 and 70 degrees C due to increase in pH (>9.5) during aging. X-ray diffraction analysis (XRD) of these samples also revealed the formation of CaCO3 at elevated temperatures with aging. While mechanisms such as Cd diffusion and/or entrapment into fissures and cracks in goethite structure with increase in temperature and aging are possible.     

Phosphorus release in aerobic sludge digestion.

The objectives of this study are to examine the phosphorus release in aerobic sludge digestion and to better understand its governing mechanisms. In this study, phosphorus release was examined using the secondary sludge from both conventional and biological nutrient removal processes. The experiments were carried out at room temperature (22 +/- 2 degrees C), with or without automatic control of pH (4.5 to 7.8), and under three aeration schemes: fully aerobic (dissolved oxygen [DO] at 3 to 4 mg/L), low DO (0.2 to 0.8 mg/L), and cyclic (with alternate on/off aeration). The released phosphorus concentrations were 20 to 80 mg/L for the conventional sludge and 60 to 130 mg/L for the biophosphorus sludge. Higher phosphorus release also occurred at low pH (<6.0). As for the effect of DO, fully aerobic digestion caused higher phosphorus release than the low-DO and cyclic operations. For better understanding, the solid phosphorus in sludge was conceptually categorized into three forms: inorganic phosphorus precipitates, organic cellular phosphorus, and polyphosphate (poly-P) in polyphosphate-accumulating organisms. Dissolution of inorganic phosphorus precipitates is controlled by physical and chemical conditions, with pH being the most important in this study. Lowering the pH to 4 to 6 clearly promoted the release of inorganic phosphorus. Polyphosphate hydrolysis, on the other hand, was found to be regulated biologically (sensitive to occurrence of anaerobic conditions) and was insignificant in the glutaraldehyde-fixed sludge. Phosphorus release from organic phosphorus should correlate with the volatile solid (VS) digestion, which lyses the cells and frees the phosphorus covalently bonded with the organic matters. The amounts of phosphorus released per unit VS digested (deltaP/deltaVS) were therefore calculated for experiments with long periods of constant pH (to minimize interferences from dissolution/precipitation of inorganic phosphorus). The results suggested that some poly-P was hydrolyzed and released accompanying the aerobic VS digestion, but at rates far lower than those under anaerobic conditions.