Effects of aging on the persistence of cadmium adsorption on organic fertilizers

Organic amendments exert important effects on the migration and transformation of cadmium in soils. However, the adsorption capacities of different types of organic amendment and the stability of the adsorbed cadmium, especially during the decomposition process, are poorly understand. Here, using adsorption kinetics, isotherm analysis and functional group analysis methods we aim to investigate the adsorption behavior of cadmium on fresh and aged (six-month-old) commercial organic fertilizers produced from sheep manure, chicken manure and tobacco waste compost. Results showed chemical adsorption was the predominant cadmium adsorption process on the organic fertilizers, especially ion-exchanged Cd (59.7% to 78.0%) and hydrogen-bonded Cd (16.5% to 37.9%). The maximum cadmium adsorption capacity occurred on the tobacco waste compost (44.7 mg g −1 ) due to the high pH and surface organic functional groups, with values of 36.6 and 18.5 mg g −1 , respectively, on the sheep and chicken manures. Similarly, increased contents of organic functional groups resulted in a higher adsorption cadmium capacity on the aged compost (50.3 mg g −1 ) than on the fresh tobacco compost (44.7 mg g −1 ), indicating that the decomposition process increased the cadmium adsorption capacity of the compost within six months. Our results suggest that aging of tobacco compost could improve its capacity for the adsorption of cadmium. Thus, application of organic fertilizer derived from tobacco waste compost would be feasible as a stable technique for the remediation of cadmium contaminated soil due to its high and persistent cadmium adsorption capacity.