与Fe(Ⅲ)共存的Fe(Ⅱ)分光光度法测定

Fe(Ⅱ)的含量及变化与土壤和沉积物的氧化还原性质关系密切.当与Fe(Ⅲ)共存时,Fe(Ⅱ)的测定往往受到干扰.本文研究了常用显色剂2,2’-联吡啶和菲洛嗪(Ferrozine)测定土壤Fe(Ⅱ)时存在的问题及解决办法.结果表明,Fe(Ⅲ)可与显色剂作用形成络合物,该络含物对Fe(Ⅱ)测定所用波段的光线具有吸收作用,从而使Fe(Ⅱ)浓度被过高估计.Fe(Ⅲ)对Fe(Ⅱ)测定的干扰程度与其浓度及所选显色剂有关.当以2,2’-联吡啶为显色剂时,单位浓度Fe(Ⅲ) (1.0 mg/L)将导致Fe(Ⅱ)的测定值比实际值高0.012 mg/L;而当菲洛嗪为显色剂时,单位浓度Fe(Ⅲ)引起的Fe(Ⅱ)高估值在0.010～0.032 mg/L之间.F-能够抑制Fe(Ⅲ)-显色剂络合物的形成.当F-的加入量超过Fe(Ⅲ)的4倍时,F-能有效地消除Fe(Ⅲ)的干扰.实际样品的测定结果表明,改进的Fe(Ⅱ)分光光度法能够满足土壤及沉积物中Fe(Ⅱ)的准确测定.     

还原态蒙脱石结构Fe（Ⅱ）催化水铁矿转化特性及影响因素

还原条件下土壤中Fe(Ⅱ)催化水铁矿转化在调控营养元素和污染物的生物地球化学过程中具有重要作用。然而,作为土壤中Fe(Ⅱ)存在的主要形态之一,蒙脱石结构中Fe(Ⅱ)催化水铁矿转化的特性及其影响因素目前尚不清楚。以化学还原的蒙脱石为研究对象,探究还原态蒙脱石(rSWy-2)结构中Fe(Ⅱ)催化水铁矿转化的特性及其影响因素。结果表明,贫铁的蒙脱石结构中Fe(Ⅱ)可催化水铁矿向纤铁矿转化,反应96 h后水铁矿转化量达到83.3%。X射线衍射(XRD)、高分辨透射(HRTEM)、球差电镜(STEM)和表面吸附态Fe(Ⅱ)含量分析表明,rSWy-2结构Fe(Ⅱ)催化水铁矿转化主要经历矿物间固相吸附、电子传递和水铁矿转化三个阶段,形成的纤铁矿呈板状纳米片,尺寸大小为100～200 nm。溶液中Na+和Cl–离子对rSWy-2催化水铁矿转化影响较弱,而Ca²⁺、SO₄^2-、有机质和As(Ⅲ)均对水铁矿转化具有明显的抑制作用。     

针铁矿-高岭石二元体的微观结构与形成机制

制备了针铁矿-高岭石复合物,以其混合物为对照,分析了它们的微观结构与形成机制。结果表明,复合物中的针铁矿较好地包被在高岭石表面,而混合物中两固相之间的包被作用微弱。相对针铁矿和高岭石两单体而言,二元体中针铁矿和高岭石的主要晶面间距没有明显变化;复合物的孔体积增多、平均孔径减小,混合物的孔体积和平均孔径都接近两单体的平均值;两种二元体的表面分形度(D)增大,且D混合物>D复合物。红外光谱显示,二元体中≡Fe-OH的振动频率升高,而≡Al-OH、Al-O、Si-O和Fe-O的振动频率降低;高岭石与针铁矿胶结后,核磁共振波谱中29Si和27Al的化学位移均向正方向移动。根据波谱分析的结果推断,针铁矿与高岭石的胶结主要通过针铁矿表面≡FenOH2(n/2)+(n=1,2,3)与高岭石表面≡Si-OH、≡Al-OH02.5+等Lewis酸之间的阳离子交换、高岭石表面≡Si-O-和≡Al-OH0.5-与针铁矿表面铁羟基(≡Fe-OH)间的阴离子交换以及高岭石表面O与针铁矿表面Fe间的配位等作用而实现,其胶结力主要为氢键和静电引力。复合物中≡Fe-OH、≡Al-OH等主要基团的振动频率以及29Si、27Al的化学位移的漂移均大于混合物中的变化量,说明复合物中针铁矿与高岭石间的胶结强度大于混合物中两固相间的胶结作用。     

与Fe(III) 共存的Fe(II) 分光光度法测定

Fe(Ⅱ)的含量及变化与土壤和沉积物的氧化还原性质关系密切。当与Fe(Ⅲ)共存时,Fe(Ⅱ)的测定往往受到干扰。本文研究了常用显色剂2,2’-联吡啶和菲洛嗪(Ferrozine)测定土壤Fe(Ⅱ)时存在的问题及解决办法。结果表明,Fe(Ⅲ)可与显色剂作用形成络合物,该络合物对Fe(Ⅱ)测定所用波段的光线具有吸收作用,从而使Fe(Ⅱ)浓度被过高估计。Fe(Ⅲ)对Fe(Ⅱ)测定的干扰程度与其浓度及所选显色剂有关。当以2,2’-联吡啶为显色剂时,单位浓度Fe(Ⅲ)(1.0 mg/L)将导致Fe(II)的测定值比实际值高0.012 mg/L;而当菲洛嗪为显色剂时,单位浓度Fe(Ⅲ)引起的Fe(Ⅱ)高估值在0.010～0.032 mg/L之间。F-能够抑制Fe(Ⅲ)-显色剂络合物的形成。当F-的加入量超过Fe(Ⅲ)的4倍时,F-能有效地消除Fe(Ⅲ)的干扰。实际样品的测定结果表明,改进的Fe(Ⅱ)分光光度法能够满足土壤及沉积物中Fe(II)的准确测定。     

pH对Cu(Ⅱ)和Pb(Ⅱ)在可变电荷土壤表面竞争吸附的影响

在实际的重金属污染体系中往往有多种重金属元素同时存在，当这一污染体系与土壤作用时不同重金属离子对土壤表面存在竞争吸附。Cu（Ⅱ）和Pb（Ⅱ）是土壤中常见的2种重金属离子，土壤和矿物表面对2种离子的竞争吸附或2种离子吸附亲和力的比较已有一些研究报道。一般认为土壤对Pb（Ⅱ）的吸附亲和力大于对Cu（Ⅱ）的吸附亲和力，但在可变电荷土壤和矿物中情况有所不同。McKenzie的结果表明合成赤铁矿在pH3．0～6．0范围内对Pb（Ⅱ）的吸附亲和力大于Cu（Ⅱ），而针铁矿的结果相反。     

Mn~(2+)掺杂对晶质氧化铁结构与红外光谱特征的影响

制备针铁矿和赤铁矿的混合晶质氧化铁(CIO)和不同摩尔比例(R)的Mn~(2+)掺杂晶质氧化铁(CIO-Mn_x(x=0.1、0.2、0.3和0.5))样品。根据样品的X-射线衍射(XRD)和透射电镜(TEM)结果分析Mn~(2+)掺杂对晶质氧化铁结构与形貌的影响;对样品的傅里叶红外图谱(FT-IR)的高波数(3 000～3 700 cm~(–1))和低波数(450～750 cm~(–1))两个区间做分峰拟合,分析Mn~(2+)掺杂晶质氧化铁的羟基官能团和晶体结构化学键的变化特征。结果显示,R为0.1～0.3的Mn~(2+)掺杂抑制了针铁矿和赤铁矿等晶质氧化铁的形成;R为0.5的Mn~(2+)掺杂导致样品中形成了掺锰磁铁矿,且存在少量的针铁矿而没有明显的赤铁矿。CIO样品中存在自由羟基、吸附水羟基、表面缔合羟基和结构羟基共四类羟基。在R为0.1～0.3范围内,随着R的增大,样品中自由羟基和吸附水羟基的相对含量降低,而表面缔合羟基和结构羟基的相对含量增大。此外,Mn~(2+)掺杂导致样品中自由羟基和结构羟基的吸收带波数降低,而吸附水羟基和表面缔合羟基的吸收带波数随R的增大而增大。CIO样品中Fe-O振动在455 cm~(–1)和619 cm~(–1)附近红外吸收带的强度和峰形与样品中针铁矿颗粒的形貌有关,478 cm~(–1)和560 cm~(–1)附近的红外吸收与样品中赤铁矿的结晶度密切相关。分析表明,CIO-Mn_x样品中的赤铁矿结构中阳离子空位与Mn~(2+)耦合产生了567～589 cm~(–1)附近的吸收,其强度随着R的增大而增强。CIO-Mn_(0.5)样品中形成了Mn~(2+)替代Fe2+的掺锰磁铁矿,导致样品在593 cm~(–1)处出现了Mn-O晶格振动吸收带。     

不同pH下两种可变电荷土壤中Cu(II)、Pb(II)和Cd(II)吸附与解吸的比较研究

对两种可变电荷土壤的研宄表明,土壤对Cu(Ⅱ)、Pb(Ⅱ)和Cd(Ⅱ)的吸附量均随pH的增加而增加,但Cu(Ⅱ)与Pb(Ⅱ)吸附量之间的差值随pH增加而减小,Cu(Ⅱ)和Pb(Ⅱ)与Cd(Ⅱ)吸附量之间的差值随pH增大呈增大趋势.土壤吸附的Cd(Ⅱ)的解吸量随吸附平衡液pH的增加而增加;但Cu(Ⅱ)和Pb(Ⅱ)的解吸量先随pH增加而增加,在某一pH时达最大,随后再逐渐减小.3种重金属离子在可变电荷土壤中吸附和解吸行为的不同特征是pH导致的土壤表面电荷的变化和离子水解程度的变化共同作用的结果.本文的研究结果对可变电荷土壤中重金属的控制和污染土壤的修复具有一定的指导意义.     

人工合成绿锈GR1(CO32−)的氧化晶质过程、特点及主要影响因素

通过空气氧化法,采用电化学实时监测,结合X-射线衍射（XRD）、透射电镜（TEM）和溶液化学分析,探讨了 GR1(CO32-)的合成、氧化和晶质化特点。在合成阶段,当悬液pH降至最低或矿物中Fe2 含量升至最高时,GR1(CO32-)完全形成。在随后转化阶段,控制pH在6.5 ~ 10时,随pH增加,GR1(CO32-)的转化速率和氧化速率均减小,氧化产物由纤铁矿向针铁矿向磁铁矿变化,且针铁矿结晶尺寸随pH升高逐渐增加。控制温度在15 ~ 45 ℃时,随反应温度的增加,GR1(CO32-)的转化速率增加而氧化速率减小,氧化产物同样由纤铁矿向针铁矿向磁铁矿变化,且针铁矿粒径随温度升高而增大。控制空气流速在0 ~ 0.1 m3 h-1时,随着空气流速的增加,氧化速率增加,氧化产物中针铁矿含量逐渐减少而纤铁矿含量逐渐增加,且产物结晶度逐渐减弱。因此,在pH、温度和空气流速等影响GR1(CO32-)转化过程中,氧化速率是共同的决定因素,随着氧化速率的增加,产物由磁铁矿向针铁矿向纤铁矿变化,且产物结晶尺寸变小和结晶度减弱。     

苹果属小金海棠Fe(Ⅱ)转运蛋白基因的克隆和序列分析

1986年,Romheld和Marschner首先提出高等植物在长期适应缺铁胁迫过程中逐渐形成的两种适应性机理。在缺铁胁迫的条件下,机理I植物通过激活一种特异的H^ -ATPase而使土壤酸化,并通过一种特异的根部还原酶将Fe(Ⅲ)还原成Fe(Ⅱ)。之后Fe(Ⅱ)通过它的转运蛋白(Transporter)跨越根部的细胞质膜而被转运。     

EDTA-2Na对改善含Fe(Ⅲ)食品中商陆色素稳定性的研究

为探索天然商陆色素在含Fe(Ⅲ)食品中的应用,以商陆果色素原液为试验材料,通过添加Fe(Ⅲ)与EDTA-2Na的方法,研究了食品中Fe(Ⅲ)对商陆色素稳定性的影响及EDTA-2Na对改善含铁食品中商陆色素稳定性的效果。结果表明：Fe(Ⅲ)会降低商陆色素的吸光度保留率及热稳定性,色素的稳定性与Fe(Ⅲ)浓度、加热时间呈负相关;在含Fe(Ⅲ)食品中添加EDTA-2Na,可改善商陆色素的稳定性,当EDTA-2Na与Fe(Ⅲ)摩尔数比大于1时,色素的吸光度保留率在85%以上;色素的稳定性与Fe(Ⅲ)和EDTA-2Na的加入顺序有关,“Fe(Ⅲ)+EDTA-2Na+色素”的加入顺序色素的吸光度保留率最高。     

Reductive dissolution of crystalline and amorphous Fe(III) oxides by microorganisms in submerged soil

Summary Reduction of Fe(III) of amorphous and crystalline Fe(III) oxides to Fe(II) in flooded soils was studied using ⁵⁹Fe(OH)₃ and ⁵⁹Fe₂O₃. The results indicated that Fe(III) in the amorphous oxide was readily amenable to microbial reduction in anaerobic soil condition whereas Fe(III) in the crystalline oxide was not. Following soil submergence, the native as well as the applied crystalline Fe(III) oxides were rapidly converted into the amorphous form. The transformation of the crystalline oxides to the amorphous form appears to be a prerequisite for the reduction of Fe(III) of the oxide. This transformation, probably through hydration, is also mediated by microorganisms.     

The relative efficiency of ionic iron(III) and iron(II) utilization by the rice plant

Uptake of iron by rice plants was equally rapid when supplied as ionic iron(II) or iron(III) at pH 3 and 4. Iron(III) uptake was reduced at pH 5 and uptake of iron when supplied as FeEDTA was relatively low at all three pH levels.

At pH 4 in the presence of plant roots, reduction of iron(III) to iron(II) occurred as indicated by Fe²⁺ BPDS formation. BPDS in a 3:1 ratio to iron(III) suppressed iron uptake by about 70%. The reduction was observed to be located in the endodermis of young roots and exodermis of older roots.

A capacity to oxidize iron(II) at the root surface was also observed under local anaerobic and relatively high pH conditions.

The significance of these two counteracting processes in affecting the oxidation state of iron at the root surface is discussed.     

Formation and properties of hydroxy iron(iii) oligomer-citrate complex

Instantaneous neutralization of Fe (III) chloride dissolved in N a citrate by powdery NaHC03 gave stable clear brown sols. The sol particles separated by dialysis and freeze-drying showed a single diffraction peak at 2 nm and a citrate/Fe molar ratio of about 0.2 irrespective of the composition of the starting solutions. This indicates that the product may be a novel phase of Fe (III) citrate.     

Studies on the magnesium metabolism of crops (Part 1) the balance among magnesium,calcium and pot assLum in free and bound forms at the flowering stage of soy-bean plants

In the later nineteenth century, it was established that magnesium is one of the essential elements to plant life. In 1902 Loew¹⁾ and his pupils suggested the necessity of calcium-magnesium- balance in culture solution for the proper growth of the plant. Then, in 1906, it was established that, as first shown by Willstatter, magnesium is one of the constituents of chlorophyll and when this element is lacking, a chlorosis occurs. Dickson²⁾, in 1918, described about the feature of oat plant grown in a magnesium deficient nutrient solution. At that time, it was thought that magnesium was generally contained in the soil more abundantly than the plant required. So this element scarcely received attention. Garner et al.³⁾, in 1923, observed that chlorosis of tobacco plant, so-called sand drown was cured by applying magnesium to the soil. Similar observation was made in 1929 by Jones⁴⁾ on the chlorosis of corn plant. Since that time the magnesium deficiency in all crops was observed everywhere by a great many investigators. In Japan magnesium deficiency in the field has attracted attention from 1951.     

Partial replacement of Fe(o,o‐EDDHA) by humic substances for Fe nutrition and fruit quality of citrus

The most widely used Iron (Fe) fertilizer in calcareous soils is the synthetic chelate Fe(o,o‐EDDHA). However, humic substances are occasionally combined with Fe chelates in drip irrigation systems in order to lower costs. We investigated the effect of various mixtures of Fe(o,o‐EDDHA) and a commercially available humic substance on Fe availability in a calcareous soil from Murcia, Spain (in vitro experiment) and on leaf Fe content and fruit‐quality attributes of Citrus macrophylla (field experiment). In the in vitro experiment, a calcareous soil was incubated for 15 d with solutions of sole Fe(o,o‐EDDHA) and humic substance and of a mixture of humic substance and Fe(o,o‐EDDHA) to determine the dynamics of available Fe. While the mixture did not significantly increase the available soil Fe, it did decrease the rate of Fe retention in the surface soil compared to sole Fe(o,o‐EDDHA). In the field experiment, the substitution in the application solution of 67% of Fe(o,o‐EDDHA) by commercial humic substance increased leaf P in lemon trees from 0.19% with sole Fe(o,o‐EDDHA) to 0.30% and leaf Fe from 94 mg kg^–1 to 115 mg kg^–1. Some quality parameters like vitamin C content and peel thickness were also improved with a partial substitution of Fe(o,o‐EDDHA) by humic substances. We conclude that a partial substitution of commercial Fe chelates by humic substance can improve crop Fe uptake and may thus be economically attractive. The underlying physiological mechanisms and ecological implications require further studies.     

天然磁铁矿和商用Fe3O4修复Hg(II)污染地下水的模拟研究

目前汞污染地下水修复面临很大的技术和成本挑战,亟需发展修复效果好、经济效益性高的汞污染地下水修复技术和修复材料。通过批量实验和光谱分析探究了天然磁铁矿和商用Fe_3O_4对Hg(Ⅱ)的去除效率和去除机制,并分析了两种材料对模拟地下水中Hg(Ⅱ)的吸附和脱附行为。结果表明,天然磁铁矿和商用Fe_3O_4对Hg(Ⅱ)的去除受pH、Hg(Ⅱ)初始浓度、Cl-等因素的影响;二者对Hg(Ⅱ)的去除均符合准二级动力学模型和Freundlich模型;天然磁铁矿对Hg(Ⅱ)的去除机制主要是羟基络合与物理吸附,而商用Fe_3O_4对Hg(Ⅱ)的去除主要是化学还原与物理吸附。二者对模拟地下水中Hg(Ⅱ)的去除率分别达90%和95%,具有修复Hg(Ⅱ)污染地下水的应用潜力。     

The competitive vs. complementary bacteria‐fungi interactions promote microbial release of Fe(III)‐fixed phosphorus: the roles of exogenous C application

The phosphorus deficiency is very common in Fe(III)‐rich soil, and one of the key point is to clarify the condition in release or desorption of phosphorus from the Fe(III)‐rich minerals. The present study was to explore the effect of labile carbon on microbial reduction of Fe(III) and release of phosphorus in root‐free sub‐tropical soil. A two‐compartment microcosm was collected, in which the roots of Medicago sativa L. cultivar ‘Aohan' were confined within one compartment by a barrier of 30‐μm nylon mesh, while mycorrhizal hyphae could penetrate to the second compartment. Arbuscular mycorrhizal fungi (Funelliformis mosseae) were added to the root compartment and iron‐reducing bacteria (Klebsiella pneumoniae) were added to the hyphal compartment. Hyphal compartments were provided with two levels of additional carbon (0 and 23 mg C kg^?1 soil as sodium acetate) and eight levels of inorganic phosphorus (0 to 35 mg P kg^?1 soil as KH₂PO₄). At low phosphorus levels (< 5 mg P kg^?1 soil), shoot biomass, and total biomass phosphorus were substantially less with added carbon in the presence of iron‐reducing bacteria. Carbon had little effect without iron‐reducing bacteria. At higher phosphorus levels (> 15 mg P kg^?1 soil), the effect of added carbon was reversed; that is shoot biomass and total biomass phosphorus were greater with added carbon. Available soil phosphorus showed a similar response to added carbon—less at low levels of phosphorus and greater at higher levels of phosphorus. Microbial phosphorus in the presence of iron‐reducing bacteria was always higher with added carbon at all corresponding levels of soil phosphorus. Taken together, these results show that some phosphorus mobilized by iron‐reducing bacteria was converted into microbiological phosphorus, but there was an obligatory requirement for labile carbon for this to happen—reducing the amount of phosphorus that was absorbed by the mycorrhizal hyphae. Iron‐reducing bacteria and mycorrhizae showed a competitive interaction at lower levels of available soil phosphorus, and a complementary, or possibly a carbon‐dependent synergistic function at higher levels of available phosphorus. These results demonstrate that phosphorus released from ferralsols by iron‐reducing bacteria is positively mediated by both phosphorus and labile carbon and, hence, that phosphorus release and mobilization by iron‐reducing bacteria is likely to be enhanced by additions of exogenous carbon.     

Selenium in amorphous iron (hydr)oxide-applied soil as affected by air-drying and pH

Occurrence of D-amino acid has been reported in various higher plants (11, 13). However detailed aspects of the synthesis and degradation of D-amino acids in higher plants are poorly documented.     

Distribution of Manganese(Ⅱ) Chemical Forms on Soybean Roots and Manganese(Ⅱ) Toxicity

Distribution of chemical forms of manganese(Ⅱ)(Mn(Ⅱ))on plant roots may affect Mn(Ⅱ)absorption by plants and toxicity of Mn(Ⅱ)to plants at its high level.The chemical forms of Mn(Ⅱ)on soybean roots were investigated to determine the main factors that affect their distribution and relationship with Mn(Ⅱ)plant toxicity.Fresh soybean roots were reacted with Mn(Ⅱ)in solutions,and Mn(Ⅱ)adsorbed on the roots was differentiated into exchangeable,complexed,and precipitated forms through sequential extraction with KNO_3,EDTA,and HCl.The exchangeable Mn(Ⅱ)content on the roots was the highest,followed by the complexed and precipitated Mn(Ⅱ)contents.Mn(Ⅱ)toxicity to the roots was greater at pH 5.5 than at pH 4.2 due to the larger amount of exchangeable Mn(Ⅱ)at higher pH.The cations Al~(3+),La~(3+),Ca~(2+),Mg~(2+),and NH_4~+competed with Mn(Ⅱ)for cation exchange sites on the root surfaces and thus reduced exchangeable Mn(Ⅱ)on the roots,in the order Al~(3+),La~(3+)Ca~(2+),Mg~(2+)NH_4~+.Al~(3+) and La~(3+) at 100μmol L~(-1) decreased exchangeable Mn(Ⅱ)by 80%and 79%,respectively,and Ca~(2+) and Mg2+at 1 mmol L~(-1) decreased exchangeable Mn(Ⅱ)by 51%and 73%,respectively.Organic anions oxalate,citrate,and malate reduced free Mn(Ⅱ)concentration in solution through formation of complexes with Mn(Ⅱ),efficiently decreasing exchangeable Mn(Ⅱ)on the roots;the decreases in exchangeable Mn(Ⅱ)on the roots were 30.9%,19.7%,and 10.9%,respectively,which was consistent with the complexing ability of these organic anions with Mn(Ⅱ).Thus,exchangeable Mn(Ⅱ)was the dominant form of Mn(Ⅱ)on the roots and responsible for Mn(Ⅱ)toxicity to plants.The coexisting cations and organic anions reduced the exchangeable Mn(Ⅱ)content,and thus they could alleviate Mn(Ⅱ)toxicity to plants on acid soils.