Degradation of Lindane by Zero-Valent Iron Nanoparticles

Thus far, zero-valent iron has been studied mostly for the degradation of structurally simple one- and two-carbon halogenated organic contaminants such as chlorinated methanes, ethanes, and ethenes. In this research, laboratory synthesized particles of nanoscale iron were explored to degrade lindane, also known as γ-hexachlorocyclohexane, a formerly widely utilized pesticide and well-documented persistent organic pollutant. In general, lindane disappeared from aqueous solution within 24?h in the presence of nanoiron concentrations ranging from 0.015?to?0.39?g/L. By comparison, approximately 40% of the initial lindane dose remained in solution after 24?h in the presence of 0.53?g/L of larger microscale iron particles. However, the surface area normalized first-order rate constants were all within the same order of magnitude regardless of dose or iron type. A key reaction intermediate, γ-3,4,5,6-tetrachlorocyclohexene from dihaloelimination of lindane was identified and quantified. Trace levels of additional degradation products including benzene and biphenyl were detected but only in the high concentration experiments conducted in 50% ethanol. While up to 80% of the chlorine from the lindane molecules ended as chloride in water, only 38% of the expected chloride concentration was observed for the microscale iron experiment. This work together with previous published studies on the degradation of polychlorinated biphenyl, chlorinated benzenes, and phenols suggest that zero-valent iron nanoparticles can be effective in the treatment of more structurally complex and environmentally persistent organic pollutants such as lindane.     

Effects of Surface-Bound Fe2+ on Nitrate Reduction and Transformation of Iron Oxide(s) in Zero-Valent Iron Systems at Near-Neutral pH

Nitrate reduction in an iron/nitrate/water system with or without an organic buffer was investigated using multiple batch reactors under strict anoxic conditions. Nitrate reduction was very limited (<10%) at near-neutral pH in the absence of the organic buffer. However, nitrate reduction was greatly enhanced if the system: (1) had a low initial pH ( ～ 2–3); (2) was primed with adequate aqueous Fe2+; or (3) was in the presence of the organic buffer. In Cases (1) and (3), nitrate reduction usually was involved in three stages. The first stage was quick, and H+ ions directly participated in the corrosion of iron grains. The second stage was very slow due to the formation of amorphous oxides on the surface of iron grains, while the third stage was characterized by a rapid nitrate reduction concurrent with the disappearance of aqueous Fe2+. Results indicate that reduction of nitrate by Fe0 will form magnetite; Fe2+ (aq.) can accelerate reduction of nitrate and will be substoichiometrically consumed. Once nitrate is exhausted in the system, no more Fe2+ will be consumed. In the presence of nitrate, Fe2+ (aq) will be adsorbed onto the surface of iron grains or iron oxides; the surface-complexed Fe(II) (extracted by acetate with pH = 4.1) might be oxidized and become structural Fe(III), resulting in a steadily increasing ratio of Fe(III)/Fe(II) in the oxides formed. The transformation of nonstoichiometric amorphous iron oxides into crystalline magnetite, a nonpassive oxide, triggers the rapid nitrate removal thereafter.     

纳米零价铁对溶液中铅镉铬砷的去除性能研究

通过液相还原法,采用KBH4还原Fe2+成功制备了平均粒径40~80nm、比表面积19.713 4m2/g、有较好表面活性的纳米零价铁(NZVI),NZVI在含铅、砷、铬、镉初始浓度为100mg/L的pH分别为2、7、12的溶液中进行去除试验。结果表明,在pH=2与pH=7的条件下NZVI对铅、砷、铬的去除效果较好,去除速率在前30min较快;在pH=12条件下对镉的去除效果明显,去除速率在前40min较快;不同pH条件下各离子的去除率差异较大,这主要与各离子在不同pH条件下的存在形态有关。NVZI去除溶液中的铅、砷、铬、镉,不仅效率高,而且绿色环保,不会对环境造成二次污染。     

碱度对热压含碳球团软熔滴落性能的影响

热压含碳球团是一种利用煤的热塑性提高冶金性能的新型炼铁原料,具有还原速度快、高温强度高、原料适应性强等优点。在固定碳氧比n(FC)/n(O)为1.00的条件下,通过改变热压含碳球团碱度,系统研究了碱度对热压含碳球团软熔滴落性能的影响。研究表明:碱度对软化区间、熔化区间、滴落率等软熔滴落性能参数有显著的影响。随着碱度的增加,软化区间t40-t4先变窄后加宽,在碱度为1.40时最窄,降至331℃;熔化区间tD-tS先缓慢变窄后急剧加宽,在碱度为1.00时最窄,降至47℃;滴落率先增加后降低,在碱度为1.20时滴落率最高,达到22.22%。从软熔滴落性能角度综合考虑,实际生产热压含碳球团时其适宜的碱度范围为1.00~1.20。     

反应气氛和温度对热压含碳球团还原反应进程的影响

热压含碳球团是利用煤的热塑性而将铁矿粉和煤粉热压成型的一种新型优质炼铁原料.还原性是炉料主要冶金性能之一,而反应气氛和温度对热压含碳球团还原反应进程有重要的影响.通过还原失重试验,重点研究了反应气氛和温度对热压含碳球团还原反应进程的影响.研究表明,热压含碳球团整个还原反应进程可分为两个阶段:第一阶段还原速率明显大于第二...