Plant Availability of Boron Adsorbed or Occulted on Goethite to Rape (Brassica napus L.) Seedling

The purpose of the study was to determine plant availability of boron (B) and relaxation of soil acid to rape seedling exhibited by B-doped goethite in acidic soil. For this purpose, two kinds of B-doped goethite were synthesized: one was goethite with adsorbed B prepared by reacting goethite with borax solution, and the other was goethite with occluded B by synthesizing goethite in the presence of boric acid. The reaction process in soil-like natural minerals of the B-doped goethite was simulated in a rhizobox culture system. Results showed that the B-doped goethite can provide available B for rape growth. Its addition on acidic soil can alleviate soil acidification by increasing soil pH and decreasing soil exchangeable acid. The observation that nutrient uptake was improved supports the view that the B-doped goethite improved soil quality, as also proved by the increase of root morphology and dry weight.     

Modeling ferricyanide adsorption on goethite: Basics and applications

Ferricyanide, [Fe^III(CN)₆]^3–, is an anthropogenic and potentially toxic contaminant in soil. Its adsorption on goethite has been previously studied, but not evaluated with a surface complexation model (SCM) considering the effects of pH and ionic strength. Therefore, we carried out batch experiments with ferricyanide and goethite suspensions with different ferricyanide concentrations (0.075 mM and 0.15 mM), ionic strengths (0.01 and 0.1 M), and pH (ranging from 4 to 7.4). Adsorption data were then interpreted with the 1‐pK Stern and the charge distribution model assuming monodentate inner‐sphere ferricyanide surface complexes on goethite (lg K = 10.6), which are known from infrared spectroscopy. Furthermore, we applied the SCM to ferricyanide adsorption in previous studies on ferricyanide adsorption in the presence of sulfate and on the solubility of Fe‐cyanide complexes in a suspension of a loess loam. The SCM correctly reflected ferricyanide adsorption in the batch experiments as well as the effects of pH and ionic strength. The SCM also described ferricyanide adsorption in the presence of sulfate, because the ferricyanide adsorption measured and that modeled were significantly correlated (R² = 0.80). Furthermore, we applied the SCM to a study on the solubility of Fe‐cyanide complexes in soil under varying redox conditions so that ferricyanide adsorption on goethite and precipitation of Fe‐cyanide complexes were considered. The actual ferricyanide concentrations were rather reflected when applying the SCM compared to those modeled in an approach in which exclusively precipitation was taken into account. We conclude that ferricyanide adsorption on goethite should be included into geochemical modeling approaches on the mobility of Fe‐cyanide complexes in subsoils.     

柠檬酸盐和磷酸盐存在下酸性磷素酶在矿物和土壤胶体上的吸附

The aim of this work was to study the influence of phosphate and citrate, which are common inorganic andorganic anions in soils, on the adsorption of acid phosphatase by kaolin, goethite and the colloids separatedfrom yellow-brown soil (YBS) and latosol (LS) in central-south China. The YBS colloid has the major claymineral composition of 1.4 nm mineral, illite and kaolinite while the LS colloid mainly contains kaolinite andoxides. The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted tothe Langmuir model. The amount of enzyme adsorbed in the absence of ligands was in the order of YBScolloid ＞LS colloid＞kaolin≈goethite. In the presence of phosphate or citrate, the amounts of the enzymeadsorbed followed the sequence YBS colloid＞kaolin＞LS colloid＞goethite. The presence of ligands alsodecreased the binding energy between the enzyme and soil colloids or minerals. With the increase of ligandconcentration from 10 mmol L-1 to 400 m mol L-1, different behaviors for the adsorption of enzyme werefound in the colloid and mineral systems studied. A sharp decrease in enzyme adsorption was observed ongoethite while gradual decreases of enzyme adsorption were recorded in the two soil colloid systems. However,no any decrease was found for the amount of enzyme adsorbed on kaolin at higher ligand concentrations.When phosphate or citrate was introduced to the system before the addition of enzyme, the ligands usuallyenhanced the adsorption of enzyme. The results obtained in this study suggested the important role ofkaolinite mineral in the adsorption of enzyme molecules in acidic soils in the presence of various ligands.     

Occurrence and Origin of Crystalline Iron Oxides in Paddy Soils Derived from Red Earth

红壤性水稻土晶态氧化铁主要为针铁矿，并伴随少量的赤铁矿．红壤性水稻土中针铁矿的铝同晶替代量明显低于其母土（红壤），而针铁矿的晶胞参数ｂ和ｃ则是红壤性水稻土高于其母土．红壤性水稻土中赤铁矿的铝同晶替代量和晶胞参数ａ则与其母土相似．．据此认为红壤性水稻土中赤铁矿来源于母土；而针铁矿部分来源于母土，部分是由原有的赤铁矿和针铁矿的还原产物重新结晶形成的．随着水稻土的发育，赤铁矿逐渐下降，最后消失；针铁矿则相对增加，同时针铁矿中铝替代量也逐渐下降     

Adsorption of glycerophosphate on goethite (α‐FeOOH): A macroscopic and infrared spectroscopic study

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the bioavailability, mobility, and fate of organic phosphates in terrestrial and aquatic environments. Glycerophosphate (GP) is a common environmental organic phosphate, however, surface adsorption reactions of GP on soil minerals have not been well understood. The adsorption characteristics of GP on goethite were studied using batch adsorption experiments, zeta (ζ) potential measurements, and in situ attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR). GP exhibited fast initial adsorption kinetics on goethite, followed by a slow adsorption. The maximum adsorption densities of GP on goethite were 2.00, 1.95, and 1.44 μmol m^?2 at pH 3, 5, and 7, respectively. Batch experiments showed decreased adsorption of GP with increasing pH from 3 to 10. Zeta potential measurements showed a remarkable decrease in the goethite isoelectric point upon GP adsorption (from 9.2 to 5.5), suggesting the formation of inner‐sphere surface complexes. In addition, the ATR‐FTIR spectra of GP sorbed on goethite were different from those of free GP at various pH values. These results suggested that GP was bound to goethite through the phosphate group by forming inner‐sphere surface complexes.     

Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. I. Effect of iron oxides on ammonium fixation

Experiments were conducted with two typical paddy soils from China and a vermiculite to study the influence of iron oxides on the fixation and release of ammonium. Removing iron oxides, especially amorphous iron oxides, from the soils favoured the release of non-exchangeable NH₄-N and stimulated the fixation of NH₄-N in the presence of added (NH₄)₂SO₄. Addition of artificial goethite and hematite to the original soils or to the soils free of iron oxides reduced the fixation of NH₄⁺-ions. This effect was also observed with vermiculite. We conclude that the coating of clay minerals with iron oxides has an impact on the diffusion of NH₄⁺-ions into and out of the interlayers of the clay minerals. The reduction and dissolution of iron oxides induced by low redox potential (E_h) after flooding of paddy soils is assumed to be an important mechanism controlling NH₄⁺-fixation in paddy fields.     

通过微量量热法研究Cd2+在针铁矿上的吸附机制

A study on energy changes and mechanisms of Cd sorbed on goethite was performed using the technique of microcalorimetry.The data of the amount of Cd sorpion(Aq) and concentration of Cd in equilibrium solution(Ce),and the data of Aq and the heat effect(AH) caused by Cd^2 sorption on goethite all fitted Langmuir isotherm.The amount of heat released from Cd sorption on goethite increased with the amount of Ce or Aq.The reaction process of Cd sorption on goethite may be divided into five stages and three plateaus,depending on the variation of enthalpy change(ΔaHm) of Cd sorption with Aq,which implied three mechanisms of interaction between Cd and goethite.The experimental results showed that the microcalorimetry may be useful for determination of microcalorie variation in soil.     

从物质的磁性看高岭土与针铁矿的胶结本质

通过对针铁矿，高岭土及其胶结样，混合样撅经率的测定和相应计算，发现胶结样中Ｆｅ＾３＋的末配对电子数较无胶结作用的Ｆｅ＾３＋的为大，为此认为其胶结本质就是生成了氢键。