نوع مقاله : مقاله کامل علمی پژوهشی
نویسندگان
1 گروه علوم خاک، دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد، ایران.
2 واحد آب و خاک، سازمان ﺗﺤﻘﯿﻘﺎت، آموزش و ترویج ﮐﺸﺎورزی، شهرکرد، ایران.
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and objectives:
Some mining activities such as extraction, transportation, processing and recycling of minerals have led to soil pollution. The common pollutant of these activities is the entry of heavy metals such as zinc (Zn) into the soil. Zn decreases roots growth and leaves development and causes chlorosis, especially in young leaves. One of the effective factors of Zn adsorption by plants is its bioavailability in soil. The availability of Zn in soil is regulated by biological, chemical, and physical processes and interaction between these processes. By adsorbing and stabilizing heavy metals, biochar is capable of removeing heavy metals from contaminated soil. In scientific studies, the speed of transmission, adsorption, and desorption of heavy metals, have the greatest importance and control their movement.
Materials and methods
In this research, the effect of various biochars compared on bioavailability and desorption kinetics of Zn, by treating contaminated soil with 2% wastes and biochars prepared from municipal waste compost, sewage sludge, sugarcane bagasse, rapeseed residues, almond hull and walnut hull, for stabilizing zinc, as a heavy metal, soil samples incubated for a period of 120 days. After the incubation period, the soil samples were collected, and the bioavailable amount of zinc was measured after extraction with DTPA-TEA. Also, the zinc desorption rate was measured in control and treatments during 504 hours.
Results
The results of this study showed bioavailable and cumulative release of Zn of treatments were significantly reduced in comparison with control. They were reduced more in soils treated with walnut hull and almond hull than oher soils. The comparison of the coefficient of determination (R2) and the standard error of estimate (SEE) showed that parabolic diffusion, power function, and first order equations had the highest coefficient of determination and the lowest standard error of estimate for control and treated soils, and therefore they have the ability to describe the rate of zinc release in soils. They had soils. K1 in the first-order equation was in the range of 0.007 to 0.009 mg kg − 1 h – 1 and a*b in the power function equation was in the range of 72.56 to 91.2 and R constant of the parabolic diffusion 52.5 to 74.9 mg kg − 1 h − 1. Based on the results of correlation studies in this research, the equations rates’ constants a and K1 (first-order equation), R (Simplified Elovich equation), b and a*b (in the power function equation) are more useful and realistic to describe the Zn release rate.
Conclusion
The biochars studied in this research had higher pH, EC and specific surface area than the raw residues and significantly reduced the zinc extracted by DTPA-TEA and the cumulative amount of zinc in the treatments. Biochars with higher specific surface area, pH and EC significantly reduced the availability and cumulative amount of zinc, so the order of reduction of availability and cumulative amount of Zn in soils was in the order: soils treated with walnut hull biochar > almond hull biochar > sugarcane bagasse biochar > Rapeseed residue biochar> Isfahan municipal waste compost biochar> Shahrekord sewage sludge biochar> Isfahan sewage sludge biochar. The use of biochars prepared from almond hull and walnut hull showed more ability for reduceing the bioavailability of Zn. So, the bioavailability of Zn decreased in soils treated with almond hull biochar and walnut hull biochar by 36.9% and 41.2% respectively compared to the control. Therefore, the greatest reduction of Zn bioavailability occurred due to the use of walnut and almond biochars. It is suggested that these two biochars will be tested in wider levels (farm levels) for purifying contaminated agricultural soils.
کلیدواژهها [English]
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