Dissolution Kinetics of Soil Kaolinite Derivative

Acid dissolutions of soil kaolinite were carried out in two series of experiments. The first series involved dissolution of kaolinite in HCl with 3 levels (I N, 2N and 3N) of acid strength at 60 °C. The aim of this experiment was to study the effects of acid strength and temperature on the dissolution rate of kaolinite. The dissolution reactions were not carried to completion. The second series was conducted at a higher temperature (80° C) but with only 1 level (2 N HCI) of acid strength was applied and the dissolution reactions were carried to completion. The second series of the experiment was designed to evaluate the congruency of Fe, Al and Si released from kaolinite. Fe and Al released from kaolinite which are expressed as Fe, Al (d/t dissolved/total) during the first series of experiment increased st nngly with time. It was approximately linear initially (T. region) and became more curvy with progressive dissolution. Dissolution rate constant (a) also increased significantly as the acid strength increased from 1N, 2N and 3N HCI. The increasing value of a is about one-half and his about two folds as acid strength increased from IN to 2N and from 1N to 3N HCI respectively. The increase of temperature however, had a more astounding effect on the dissolution rate. The dissolution temperature change from 60 °C to 80 °C resulted in the dissolution rate being lifted 4.5 and 3 folds for Fe and Al respectively. The dissolution data within the limited initial linear region (TO of the first series of the experiment appeared to have fitted well to the cube root law. However, it inadequately described the dissolution data of the second series where the dissolution reactions were conducted to completion. For complete dissolution reactions, dissolution kinetics is best described with the modified first order of the Kabai\u27s equation. Regression analysis shows that there is no significant relation between (a) and the properties of kaolinit analysed in this experiment. In contrast with the standard Georgia kaolinite, it has been found that for soil kaolinite the release of Fe, Al and Si occur at identical rate. Therefore, the dissolution is congruent which indicates that Fe, Al and Si in kaolinite under the present study are distributed uniformly within the crystal grains. Disolusi kaolinitdi dalam asam inorganik (HCI)dilalcsanalcan dalam dua seri penelitian. Pada seri pertama, kaolinit di la rutkan dalam HCI dengan tiga tingkatan normalitas asam, yaitu HC11N, Ha 2N, dan HCl 3N pada suhu reaksi 60°C. Penelitian pada tahap ini bertujuan untuk menilai pengaruh kepekatan asam dan suhu reaksi terhadap percepatan reaksi (a) pelepasan Fe dan Al dari kaolinit. mengetahui kesaamaan atau ketidak samaan percepatan pelarutan Fe, Al dan Si dari kaolinit. Disolusi Fe dan Al yang di hisabkan sebagai Fe(d/tâ dissolved/tolal) dan Al(c1/ t) meningkat tajam sejalan dengan meningkatnya waktu reaksi. Peningkatan tersebut lebih kurang tinier pada saat-saat awal reaksi (sekitar 50 % unsur terlarutkan â T50) dan kemudian cenderung mendatar sejalan dengan meningkatnya waktu reaksi. Percepatan reaksi juga meningkat dengan meningkatnya Icepekatan asam yang digunakan. Percepatan reaksi pelepasan Fe dan Al meningkat sekitar satu setengah kali lipat apabila kepekatan asam ditingkatkan dari IN 14C1 menjadi 2N HC1, dan menjadi dua kali lipat apabila kepekatan asam ditingkatkan dari 1 menjadi 3N HC1. Peningkatan suhu reaksi berpengaruh kWh hebat lagi. Apabila suhu reaksi ditingkatkan dari 60°C menjadi 80°C maka percepatan reaksi pelepasan akan meningkat sekita r 15 kali lipat untuk Fe dan sekitar 8 kali lipat untuk Al. Persa mann cube-root ma mpu menggambarkan reaksi disolusi Fe dan Al dengan amat balk pada daerah hampir linear(T,o) pada percobaan seri pertama. Tetapi untuk seri kedua, dimana reaksi disolusi sampai sempurna, kinetikdisolusi dari Fe, Al dan Si dari cuplikan pada penelitian ini paling baikdigambarkan dengan persamaan Kabai. Analisis regresi memperliliatkan bahwa tidal( terdapat hubungan yang signifikan antara (a) dengan sifat-sifat Icaohnit yang teranalisis pada penelitian ini. [Key words: kaolinite, dissolution, kinetics

Relationships of water repellency to soil properties for soils of southwestern Australia

In order predict the susceptibility of soils to the development of water repellency, it is necessary to identify predictive relationships between water repellence and commonly measured soil properties. This paper evaluates these relationships for diverse groups of soil samples. The soil assemblages include a set of reference soils from the south west of Western Australia (an area of 250 000 sq km), more intensively sampled suites of soils in several smaller soil landscape associations within the south west of Western Australia (≈1000 sq km), soils from single farms (1-10 sq km) and transects(≈0.001 sq km) and single soil profiles(≈sq m). The severity of water repellency was assessed by measuring water drop penetration time in seconds (WDPT) and was statistically related to intrinsic properties of soils using log transformed data. For the set of soils from the West Midland Sandplain the type of land use was also considered. There is a general tendency for WDPT to increase as organic matter content increases and decrease as the content of fine mineral material increases (clay, silt, fine sand). However there is no single soil property that is able to adequately predict WDPT. Furthermore reliability of prediction decreases as the area of sampling increases. There appear to be no systematic differences in the capacity of organic matter from pasture or crop to induce water repellency but increments of organic matter under bush increase water repellency at a greater rate than does organic matter from crop or pasture

Use of soil survey data for spatial modelling of potential wheat yield

To date, estimates of potential wheat yield have been based on the concept of effective growing season rainfall. This approach has been used to provide growers with a 'target' that could be achieved with appropriate management. There is evidence to suggest that targets set by this approach are unrealistically high, particularly in Western Australia. Reasons for this include failure to account for water loss by deep drainage and failure to adequately partition water loss by soil evaporation from plant transpiration which drives the biomass production. Physically-based water balance models with appropriate plant growth functions can address these problems and provide a potential yield estimate based on transpired water. In this paper we present some examples of this approach and illustrate how soil survey data can be used to provide the necessary parameters for the water balance model. The method is used to provide a preliminary assessment of potential yield for the Lake Carlocup area near Jerramungup. We show in particular that the spatial pattern of transpiration and hence potential yield is not stationary from season to season. This observation has implications for interpretation of patterns observed in precision agriculture trials

Aeolian influences on the soils and landforms of the southern Yilgarn Craton of semi-arid, southwestern Australia

Within a landscape developed on the deeply weathered, dominantly granitic rocks of the Yilgarn Craton in southwestern Australia, there is strong evidence of prior aeolian activity. Multiple arrays of clayey saltation deposits occur as clay dunes or lunettes extending up to 5 km to the southeast of playas, and quartzose sand dunes and sheets occur in a 2-km wide band that extends 10 km southeast of an ephemeral creek line. Parabolic dunes occur within some clayey lunettes. The parallel orientation of these diverse features and the elliptical shape of the playas suggest that the winds that have created these geomorphic entities have been from the northwest. Multiple lunette arrays with up to seven members have not been previously reported in this region.There is evidence for a more widespread, but more subtle, aeolian influence on the soils. Dust deposits appear to mantle parts of the landscape and are inferred to be coeval with the clayey saltation deposits. Although these do not occur as a discrete layer, evidence includes a plume of calcareous and illitic soils southeast of the major playa, in a landscape otherwise characterised by acidic, kaolinitic soils. Similarly, the occurrence of deep sandy soils on many slopes with a southeasterly aspect may indicate the interference of topography on the transport of saltating sands during an arid climatic phase. The presence of such aeolian deposits has implications for agricultural management, mineral exploration and the interpretation of ecological gradients in similar undisturbed landscapes.Current desertification, in the form of salinization and wind erosion, has precedence in this landscape. The aeolian deposits provide a means of interpreting landscape-scale responses to previous climate change and a key to predicting possible outcomes of both desertification and future climate change. Assuming that Bowler's theory that clay dunes require an adjacent salinized playa bed to form is correct, the arrays of clayey lunettes together with vegetated former playas indicate that the landscape has undergone multiple cycles of salinization and recovery. The lunettes may thus provide a means of predicting landscape hydrological responses to the widespread removal of natural vegetation for farming. Dating of the various sequences is required to provide a time scale for these landscape processes

Soil attributes related to water repellency and the utility of soil survey for predicting its occurrence

The incidence and severity of water repellency was related to five soil class (FC I-V), based on the field texture and dry consistence of the soil surface horizons, derived from a soil survey near Jerramungup, Western Australia. Water repellency was most severe on the FC I soils (median clay content 1.5%), with 66% of samples having water repellency based on the water drop penetration time (WDPT) test >10 s. Corresponding values for the FC II and III soils (2.5%, 4.0% clay) were 37% and 20%. Water repellency did not occur on the most clayey FC IV (8.1% clay) and FC V (22.1% clay) soils. Following stratification of Ap horizon soils by 1% increments of clay content, highly significant linear relationships occurred between log [water drop penetration time (WDPT)] and log [organic carbon (OC)] for the 1-2, 2-3 and 3-4% clay classes, these respectively explaining 50, 35 and 37% of the variation in water repellency. The role of organic carbon in promoting water repellency decreases markedly with increasing clay content, with WDPT being proportional to OC4.5, OC3.9 and OC3.0 for each of these clay classes. A multivariate relationship using measures of amorphous iron, clay and organic matter explained 63% of the variation in water repellency, and this multivariate dependency provides an explanation of the poor bivariate relationships between either clay or organic carbon content and water repellency reported in previous studies. There is a strong geomorphic control of the clay content in the soil surface horizons. Given the effect that clay content has on water repellency, the susceptibility of soils to water repellency can be mapped across farms, with the actual expression of water repellency depending on soil organic matter content, and hence land use. Such discrimination will allow the prediction of water erosion hazard and identify soils requiring ameliorative treatments