Adsorption of Oxamyl and Dimecron in Montmorillonite Suspensions

Abstract

Adsorption of oxamyl and phosphamidon (Dimecron) was determined from dilute solutions of montmorillonite saturated with different cations, e.g., Li+, Na+, K+, Cs+, Fe3+, and Al3+. Adsorption of oxamyl was found to be greater than adsorption of Dimecron. The shapes of the isotherms depended on the exchangeable cations. The adsorption varied directly with the polarizing power of the exchangeable cation and inversely with changes in temperature, organic matter, and ionic strength up to 0.6, after which it became constant. The enthalpy changes (ΔH°) calculated from the temperature coefficient of the equilibrium constant showed that the process is exothermic. The adsorption of pesticides on montmorillonite gives rise to an entropy loss that is higher for trivalent cations. Various studies, e.g., infrared (IR) and x‐ray, as well as thermodynamic parameters and Freundlich adsorption isotherms, revealed the existence of protonation or coordination (or both) between exchangeable cations of clay and oxygen of > C=0 group of the pesticides. However, desorption studies showed the presence of physical adsorption.

Adsorption of Organic Chemicals in Soils

“…It can also be due to the repulsion of protonated molecules by preventing the formation of a complex. Oxamyl and dimecron adsorption on montmorillonites may be explained in this way (55).…”

“…This means that molecules are most likely to be adsorbed in a flat position and that they do not suffer a strong competition from solvent molecules (14). Ex (55) various soils and sediments adsorb solutes according to L-isotherms. Table 2 gives some examples of systems (16) and Figure 5 shows an illustration of the corresponding (62) results.…”

“…Organic cations of interest belong to two groups of compounds: compounds with a permanent charge such as bipyridinium herbicides (5,18,51); weak bases with pKa values between 3.0 and 8.0 allowing ionization by protonation in normal soil pH range. This is the case of some triazine herbicides (52,53) and of some carbamate fungicides (54) oxamyl and dimecron (55) and benzidine (56).…”

The Effects of composts on adsorption-desorption of three carbamate pesticides in different soils of Aligarh district

“…Carbamate pesticides are widely used as insecticides, nematicides and herbicides (Hague, 1979). Investigations on the adsorption of carbamate pesticides by clays have shown that they are adsorbed by co-ordination and/or protonation at the carbonyl oxygen by exchangeable cations of clays (Bansal 2009(Bansal , 1983Li et al, 2003). The purpose of the present study is to study the effect of different amount of organic manure (FYM, sewage sludge and poultry manure) on the extent of adsorption/desorption of three polar water soluble carbamate pesticides; …”

Method for Estimating Competitive Adsorption of Herbicides on Soils

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The major focus of these studies has been adsorption and desorption. [8][9][10][11][12][13][14][15][16][17][18] Mixed herbicides are applied to soils as a method of weed control in fields. However, the effects of the herbicides may differ with their interactions with the soil and with each other.…”