DETERMINING THE LENGMUR COEFFICIENT OF THE FILTRATION PROBLEM

Filtration of suspension in a porous medium is actual in the construction of tunnels and underground structures. A model of deep bed filtration with size-exclusion mechanism of particle capture is considered. The inverse filtration problem - finding the Langmuir coefficient from a given concentration of suspended particles at the porous medium outlet is solved using the asymptotic solution near the concentrations front. The Langmuir coefficient constants are obtained by the least squares method from the condition of best approximation of the asymptotics to exact solution. It is shown that the calculated parameters are close to the coefficients of the model, and the asymptotics well approximates the exact solution

Retention and release of diquat and paraquat herbicides in soils

The sorption and desorption behaviour of diquat and paraquat, in the presence of different salt concentrations, has been studied in some Western Australian soils varying in physical and chemical properties. Sorption isotherms were found to be of the 'L' type according to the Giles classification with the data fitting well to the Langmuir equation. The sorption capacities of soils for diquat ranged from very high in clay soil (146 400 �mol kg-1) to very low in sand (1765 �mol kg-1) and followed the order of clay content in the soils. The clay soil also showed the highest value for the Langmuir coefficient representing bonding energy. The sorption capacities for the herbicides were less than the CEC of the soils. Both the type and content of clay minerals present in soil were important for sorption and subsequent desorption of the dipyridylium herbicides. An increase in the salt concentration of the soil solution (from 0.005 to 0.05 M CaCl2) resulted in decreases in sorption capacities for the herbicides ranging from some 17% to 40% in the different soils. Both Ca2+ and Na+ cations competed for the sorption sites with the herbicides, but Na+ was not as effective as Ca2+. Desorption of the herbicides was also significantly affected by the salt concentrations of the extractant. After five successive extractions with 0.005 m CaCl2, the total amounts of equilibrium sorption desorbed from the Bassendean surface soil were 13% and 7% for diquat and paraquat, respectively. The percentages of diquat removed by extractions decreased with increasing clay contents in the soils studied. Desorption of diquat was higher than that of paraquat at all salt concentrations. Hysteresis was evident between sorption and desorption isotherms.. As sorption increased, the desorption became easier, indicating that the herbicides were less strongly held. Sorption which occurred in the presence of higher ionic strength solutions of inorganic cations was relatively less susceptible to desorption.

Interfacial interactions between aqueous solutions of 4,4'-bipyridyl and mercury

From analysis of electrocapillary curves obtained by drop-time measurements with spindle-type capillary and the method of controlled convection the data on reversible equilibrium adsorption of 4,4'-bipyridyl on mercury from aqueous 0·1M solutions of Na2SO4 and H2SO4 were obtained. In neutral solution 4,4'-bipyridyl is strongly adsorbed: at potential of maximum adsorption the Langmuir coefficient β = 1.4 . 102 m3 mol-1 and Γm = 1.8 . 10-6 mol m-2; in acid solution the adsorption of the doubly protonated 4,4'-bipyridylium cation is weaker and its potential dependence goes through a minimum. The increase of adsorption of the bipyridylium cation and a simultaneous increase of negative charge with increasing negative potential are explained by charge transfer in adsorbed state. The electroreduction of 4,4'-bipyridyl is preceded by formation at the electrode surface of a layer of sparingly soluble salt of the bipyridyl cation radical.