Searching for optimum adsorption curve for metal sorption on soils: comparison of various isotherm models fitted by different error functions

Studies comparing numerous sorption curve models and different error functions are lacking completely for soil-metal adsorption systems. We aimed to fill this gap by studying several isotherm models and error functions on soil-metal systems with different sorption curve types. The combination of fifteen sorption curve models and seven error functions were studied for Cd, Cu, Pb, and Zn in competitive systems in four soils with different geochemical properties. Statistical calculations were carried out to compare the results of the minimizing procedures and the fit of the sorption curve models. Although different sorption models and error functions may provide some variation in fitting the models to the experimental data, these differences are mostly not significant statistically. Several sorption models showed very good performances (Brouers-Sotolongo, Sips, Hill, Langmuir-Freundlich) for varying sorption curve types in the studied soil-metal systems, and further models can be suggested for certain sorption curve types. The ERRSQ error function exhibited the lowest error distribution between the experimental data and predicted sorption curves for almost each studied cases. Consequently, their combined use could be suggested for the study of metal sorption in the studied soils. Besides testing more than one sorption isotherm model and error function combination, evaluating the shape of the sorption curve and excluding non-adsorption processes could be advised for reliable data evaluation in soil-metal sorption system.

Sulfate sorption measured by a buffering index over a range of properties of soils from south Western Australia

Sulfate sorption by the soil affects the rate of sulfate leaching, which impacts on the availability of soil sulfate for plant uptake. In Australia, plant-available sulfur is measured using 0.25 M KCl heated for 3 h at 40°C to extract soil sulfur (SKCl40). This paper describes a technique referred to as a sulfate buffering index (SBI), which provides a measurement of sulfate sorption. SBI when combined with the estimates of the q and b parameters of the Freundlich equation, can be used to define a sorption curve. The equation is S = acb – q; where S is the amount of sulfate adsorbed (mg S kg–1), c is the equilibrium concentration of sulfate measured in solution (mg S L–1) and a, b and q are coefficients that describe the soil sulfate sorption curve. Coefficients S and c were measured using six sulfate solution concentrations ranging from 0 to 250 mg S kg–1. The adsorption curve was fitted using the modified Freundlich equation including setting of b = 0.41 and q = SKCl40 using recently collected soil samples. The modified Freundlich a coefficient or SBI was calculated as SBI = (S + SKCl40)/c0.41; where S and c were determined using 50 mg S kg–1 of added sulfate. The SBI ranged within 1–40. The SKCl40 was related to SBI below a depth of 10 cm (r2 = 0.71) but not for the 0–10 cm soil layer where S sorption was minimal.

Innovative Environment-Saving Technology Using Magnetic Sorbents Based on Carbon-Containing Waste from Coal

One of the most effective methods of oil removal from the water surface is sorption with solid sorbents. The issue of oil sorption by magnetic sorbents based on carbon-containing waste from coal, woodworking and livestock enterprises is considered in the article. In the course of the experiments, the time of sorption equilibrium onset was determined, a sorption curve was constructed, and its form was determined. According to the study, it is revealed that the developed magnetic sorbents have a maximum oil capacity of 3 g/g and show a high affinity for oil.

Comparing simple methods for measuring phosphate sorption by soils

Phosphate sorption curves were measured for 103 Western Australian soils sampled from farmers’ fields. A measure of phosphate buffering obtained from a fitted curve was compared with indexes obtained from single-point measurements of phosphate sorption. The single-point indexes were adjusted for the phosphate present in the sampled soils by adding the phosphate extracted by the bicarbonate reagent to the measured sorption. Iron and aluminium extracted by an oxalate solution were measured as indirect indexes. The single-point indexes were closely correlated with the values obtained from the sorption curve. Their correlation was much larger than that of indirect measures.

Towards a single-point method for measuring phosphate sorption by soils

Data from 4 separate studies using widely differing soils were used to assesswhether single-point estimates of the relative buffering could be used asestimates of buffering derived from fitted curves. The relative bufferingcapacity of soils for P was summarized using the ‘O&Svalue’. This is the increase in P sorption between concentrations of 0.25 and 0.35 mg P/L.Phosphate sorption curves were described by the modified Freundlich equation:S = acb – q, whereS ( g/g) is the measured sorption,c ( g/mL) the solution concentration, anda, b, and qare parameters. The fitted O&S value is given by:a (0.35 b – 0.25b ). If a single pair of values for sorption andconcentration is measured, rather than a sorption curve, thea value can be estimated from (S+ q)/cb . An estimate of the O&S value can beobtained from (S + q) (0.35b – 0.25 b)/c b .Because the b parameter occurs in both the numerator andthe denominator, the single-point estimate of the O&S value was notvery sensitive to the value allocated to b provided thevalue of c was in the range 2–5 mg P/L. Formost of the soils of low to moderate buffering, the P extracted by the Colwellreagent was a useful estimate of q. For these soils, thesingle-point estimates using this value of q weresimilar to the values found from the fitted curves. One group of exceptionswere some soils of low buffering which had received a single application ofphosphate at a high rate. For these soils, the Colwell reagent extracted largeamounts of phosphate. Another group of exceptions were soils of highbuffering. For these the Colwell reagent gave values much lower than thefitted value of q and was of little value in improvingthe calculation of single-point estimates. The single point estimates forthese soils were about 20% too low but nevertheless well correlatedwith the values from the fitted curves.

Effect of Lay-Up on the Sorption Behaviour of Woven Glass-Polyester Composites

The effects of the lay-up on the water diffusion behaviour of hand made woven glass/polyester composites have been investigated by means of sorption experiments and numerical simulation of the diffusion process in a stratified media. Experimental sorption curves exhibited a non linear behaviour during the initial sorption step. On the basis of the numerical simulations, this behaviour was attributed to an enhanced diffusion rate in the superficial matrix layers. These effects were found to affect significantly the measurement of the diffusion coefficient from the sorption curve.

The P fertilizer requirements of subterranean clover, and the soil P status, sorption and buffering capacities from two P analyses

The phosphorus fertilizer requirement of subterranean clover (Trifolium subterraneum) was determined on a number of soils in field and glasshouse experiments. The solution phosphorus concentration in a 0.01 M CaCl2 extract (SPC0) determined from a phosphorus sorption curve was found to be closely related (R2 = 0.80 to 0.84) to relative yield. The critical SPC required to achieve 90% of relative yield (SPCc) was 0-128 �g P mL-1 in the field and 0.106 �g P mL-1 in the glasshouse experiments. Phosphorus sorbed at an SPC of 0.10 �g P mL- l (Ps0.1 at SPC0.1) was highly correlated with the phosphorus requirement of subterranean clover in both the field and glasshouse, accounting for 89% and 73% respectively of the variation in phosphorus requirement. A modified two-point sorption curve was found to give a good estimate of phosphorus sorbed at both SPC0.1 (Ps0.1) and SPC0.3(Ps0.3), and greatly increased the number of soil samples that can be processed, compared with a five-point sorption curve. The two-point test involved the addition of solutions containing 0 and 8 �g P mL-1 at a soil: solution ratio of 1:10. The sorption curve constructed using this method was suitable for assessing soils with Ps0.1 levels up to 90 �g P g-1. The soil phosphate buffering capacity at SPC0.1 (PBC0.1) was also accurately estimated using calculations from the two data points, but PBC0.3 values were poorly estimated. It was concluded that the two-point sorption curve is a sensitive and efficient method of predicting the present phosphorus status of clover pastures, their phosphorus fertilizer requirements, and of calculating PBC0.1, a useful soil characteristic.

Étude des variations de radiosensibilité des semences d'orge (Hordeum vulgare) en fonction de la teneur en eau

The study of the sorption curve representing the development of water content versus relative humidity, in barley seeds (cv. Thibaut), shows that water is present in three different states: constitutive water at less than 8.1%, absorption water between 8.1 and 10.9%, and free water at more than 10.9%. Along with these water states, radiosensitivity is respectively high, low, and high. The seeds detached from the rachis have less radioresistance than the attached ones. However this difference in behaviour is reduced when the water content is high (presence of free water). We also observed that growth was stimulated by weak doses of irradiation (20 Gy), whatever the water content. Key words: barley, Hordeum vulgare, radiosensitivity, water content, seeds, rachis.

THE INFLUENCE OF TEMPERATURE ON THE SORPTION OF SODIUM HYDROXIDE ON WOOD

The sorption of sodium hydroxide on black spruce has been measured at 20°, 50°, and 75 °C., and was found not to change very much between 20° and 75°. An increase in temperature causes the break in the sorption curve to occur at a higher concentration of alkali. Cooking action begins between 50° and 75°, and tends to obscure the effect of an increase in temperature above 50°.

SORPTION OF WATER AND ALCOHOL VAPORS BY CELLULOSE

Measurements were made of the amount of water vapor sorbed by beaten and unbeaten samples of kraft, unbleached sulphite and bleached sulphite wood pulps at relative vapor pressures ranging from 0 to 100%. Beating of the pulp made practically no difference to the degree of sorption at any relative vapor pressure. This indicated that beating caused no change in the hydration of the cellulose. Measurements were made of the sorption of methyl alcohol vapor by bleached sulphite, kraft and groundwood, and of the sorption of propyl alcohol vapor by bleached sulphite and cotton, all previously wetted with water and then dried. After sorption of alcohol, evacuation at room temperatures did not completely remove the alcohol. Measurements were also made of sorption of propyl alcohol by bleached sulphite and by cotton which had been dewatered by washing with propyl alcohol. The shape of the sorption curve was different for these samples, and the residual alcohol after evacuation was less. After a sample of cotton had been dried over phosphorus pentoxide in vacuo for a long period it was found to hold 0.35% of water by weight which could be removed by heating the cellulose to 100 °C. This was regained from the pentoxide on cooling the cellulose.The data are explained on the hypothesis that the crystalline submicroscopic elements of the cellulose structure are drawn together by internal tensile forces during the evaporation of the sorbed liquid, and that bonding between these elements may take place by the growing together of the crystal elements, leaving the structure internally stressed. On absorption, dissolution of these bondings takes place and the stresses are relieved as liquid enters the structure.