Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

Adsorption density,mobility and limit values of Cd,Zn, Cu and Pb in acid forest soils

To investigate Cd, Zn, Cu and Pb adsorption in acidified forest soils, six soil samples of the aluminium buffer range were selected and analyzed for their physical and chemical properties. Determination of the specific surface area using ethylene glycol monoethyl ether (EGME) adsorption yielded a characteristic value of the solid phases, which can parameterize the major properties of the various soil constituents with sufficient accuracy.

Traditional adsorption isotherms reveal the relation between the amount of a heavy metal adsorbed and the heavy metal concentration in the soil solution only for the soil under study and can therefore not be applied to other soils. To meet the aim of modelling heavy metal adsorption and mobility also for soils differing greatly in their properties, it was attempted to establish a generalizing adsorption isotherm for soils of entirely different composition of the solid phase. The generalizing adsorption density isotherms introduced in the following provide a useful mathematical model for the quantity/intensity relation of heavy metals in soils that differ greatly in their specific surface area and their composition.

It is also shown that limit values which take into account the major quantities influencing heavy metal adsorption and mobility in acid soils can be established from the regression equation between the adsorption density of a heavy metal (ions/m² specific surface area) and its concentration in the soil solution. In particular in view of the groundwater contamination to be expected if acid rain and, as a result, soil acidification continues, these limit values seem to provide considerably more information than the European limit values, given in mg heavy metal /kg soil, which are presently valid for any soil condition and property.     

多氯联苯同系物在水稻土中的吸附行为比较

土壤是事关农产品生产环境质量安全的重要环境介质,同时因持久性有毒污染物多氯联苯(polychlorinated biphenyls,PCBs)在世界范围内普遍检出而备受科学界与政府关注。Ren等首次在中国范围内调查了52个采样点处表层土壤中的PCBs浓度,在其所有采样点处的PCBs平均浓度为     

Sorption of Phosphorus from Swine,Dairy, and Poultry Manures

In most phosphorus (P) sorption studies, P is added as an inorganic salt to a predefined background solution such as calcium chloride (CaCl₂) or potassium chloride (KCl); however, in many regions, the application of P to agricultural fields is in the form of animal manure. The purpose of this study, therefore, was to compare the sorption behavior of dissolved reactive P (DRP) in monopotassium phosphate (KH₂PO₄)–amended CaCl₂ and KCl solutions with sorption behavior of DRP in three different animal manure extracts. Phosphorus single‐point isotherms (PSI) were conducted on eight soils with the following solutions: KH₂PO₄‐amended 0.01 M CaCl₂ solution, KH₂PO₄‐amended 0.03 M KCl solution, water‐extracted dairy manure, water‐extracted poultry litter, and swine lagoon effluent. The PSI values for the dairy manure extract were significantly lower than the CaCl₂ solution for all eight soils and lower than the KCl solution for six soils. The PSI values were significantly higher, on the other hand, for poultry litter extract and swine effluent than the inorganic solutions in four and five of the soils, respectively. Our observations that the sorption of DRP in manure solutions differs significantly from that of KH₂PO₄‐amended CaCl₂ and KCl solutions indicates that manure application rates based on sorption data collected from inorganic P salt experiments may be inaccurate.     

粘土固化注浆帷幕对重金属离子的吸附特性

采用醋酸铵反复作用法测得了不同配比粘土固化浆液结石体的阳离子交换容量,利用原子吸收分光光度仪测定溶液浓度,通过室内吸附平衡实验研究了粘土固化注浆帷幕对重金属离子的吸附特性.结果表明:粘土固化注浆帷幕对Pb2 和Cd2 的吸附能力与浆液配比密切相关,在室温和pH 5.0条件下浆液组分中水泥与粘土质量比为2∶4时吸附能力最强;实验条件下Pb2 的吸附量大于Cd2 ;Pb2 和Cd2 之间存在竞争吸附,Pb2 的竞争吸附系数大于Cd2 ,且Pb2 的吸附速率大于Cd2 ;粘土固化注浆帷幕对Pb2 和Cd2 的吸附过程符合Freundlich等温吸附曲线模型,相关系数在99%以上.     

玉米豆粕混合水活性等温吸附曲线研究

试验研究了玉米、豆粕混合后水活性等温吸附曲线。结果表明:Henderson模型拟合玉米、豆粕9:1、6:4混合水活性等温吸附曲线效果最好,Chungpfost模型拟合玉米、豆粕8:2、7:3、5:5混合水活性等温吸附曲线效果最好,并由最佳拟合模型计算出不同玉米、豆粕按不同比例混合后的绝对安全水分和相对安全水分含量,其数值分别为10.596%和12.507%、10.251%和12.337%、10.342%和12.736%、10.323%和12.446%、10.558%和12.689%。     

Moisture sorption isotherms, heat of sorption and properties of sorbed water of raw bamboo (Dendrocalamus longispathus) shoots

Moisture sorption isotherms of raw bamboo shoot were determined by static gravimetric technique based on isopiestic transfer of water vapor at 20, 30 and 35 °C. Inorganic saturated salt solutions in the range of 11.2-97.2% were used to create the required controlled humidity environment in a closed chamber. In the study, the sorption isotherms obtained were of sigmoid shape and of BET II type classification. Out of three sorption models i.e., BET, Caurie and GAB, fitted to the experimental data, Caurie model was found superior in interpreting the moisture sorption characteristics of bamboo shoot at three temperatures. The monolayer moisture content M_m as estimated by the best fitted Caurie's model for the sorption processes were 6.012%, 5.801%, 5.014%, and 5.987%, 5.816%, 4.998% (dry basis) at 20, 30, and 35 °C, respectively. The isosteric heats of sorption for both the adsorption and desorption process of bamboo shoots were found to increase with decrease in moisture content suggesting endothermic reaction at lower moisture content and it approached the value of heat of vaporization of free water at higher moisture content.     

Distribution of Water between Wheat Flour Components: A Dynamic Water Vapour Adsorption Study

The water adsorption properties of hard and soft wheat flours and flour components (starch, damaged starch, gluten, soluble pentosans, and insoluble pentosans) were determined at 25 °C using a controlled atmosphere microbalance. At different levels of relative humidity (from 10% to 95%), changes in sample mass (i.e., water gain) were continuously measured versus time and described using exponential models (R²≥0·994). Water adsorption isotherms were constructed for wheat flours and flour components and described using Guggenheim-Anderson-de Boer models (R²≥0·997). It was not possible to distinguish between the selected hard and soft wheat flours by their isotherms. The water-soluble pentosans had the highest water adsorption capacity. The theoretical distribution of water between the flour components (calculated using the Guggenheim-Anderson-de Boer parameters) was starch, 88%; gluten, 10%; and pentosans, 2%.     

Phosphorus sorption curves for evaluating phosphorus requirements of loblolly pine (pinus taeda)

Abstract

Bray P2, Mehlich 1, and Mehlich 2 methods identified soils on which loblolly pine would respond to P fertilizer in a greenhouse study using six soils from the West Gulf Coastal Plain. The P extracted by any of the three methods did not correlate with growth on unfertilized soils or to the maximum amount of response when P was applied.

Phosphorus sorption curves were used to estimate the amount of P in soil solution. The concentration of P in roots and tops was proportional to the log of the amount of P in solution. For 90% of maximum dry weight of loblolly seedlings, about 0.22 mg/liter of P in soil solution was necessary. The phosphorus sorption method has the potential of predicting the P requirements of loblolly pine, but field testing is necessary.