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This study was carried out to obtain quantitative relationships between Zn in equilibrium solution and that retained by 20 calcareous soils. Soils were brought into equilibrium with varying solution concentrations of Zn, and the amounts removed from solution were used to check the fit to six adsorption isotherms, namely, Freundlich, Langmuir, Temkin, Gunary, two surface Langmuir and Adjusted Freundlich. Zinc sorption and desorption data showed hysteresis which indicates adsorption and desorption mechanisms not being the same. Fits of adsorption equations showed that Freundlich equation did not describe Zn sorption in most of the soils at low equilibrium concentrations, but after removal of the three first concentration points this equation showed a best fit to the data. The single surface Langmuir equation did not describe Zn sorption data, but a two surface Langmuir equation showed statistically significant fits to the data for some of the selected soils. Temkin equation described data only at low equilibrium concentrations.

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The kinetics of Zn sorption by ten calcareous soils of Iran were measured and fitted to several equations (zero-, first-, second-, third-order, parabolic diffusion, simple Elovich, and exponential equations). Two initial concentrations of zinc i.e. 20 and 80 mg Zn l-1 were used and observations were carried out for 100 hours. The time required to reach the near equilibrium state was about 24 hours, by which time most of the Zn in solution had been sorbed. Zero-order, first-, second-, and third-order equations did not adequately describe zinc sorption kinetics. Both simple Elovich and exponential equations did adequately describe the data. Regression analysis indicated that the total CaCO3, active CaCO3, clay content, and specific surface area were closely related to the coefficients of these two equations. The magnitude coefficients of the equations were positively related to these soil properties. Thus, Zn sorption kinetics can be predicted from data collected during routine soil evaluation.

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Converting feedstock into biochar is a popular approach to overcome the disposal problem, yet the role of waste type and pyrolysis temperature on biochar properties is not understood well. In this study, biochars were produced from various feedstock such as tea waste, apple wood, wheat straw and walnut shell at 300, 400, 500 and 600°C with 1-hour residence time. The results showed that increase in pyrolysis temperature significantly decreased biochar mass yield. The maximum and minimum mass yields were observed in walnut shell at 300˚C and apple-wood-derived biochars at 600˚C by 69 and 20%, respectively. The produced biochar had pH range between 5.3 to 9.7, and its pH value and ash content increased significantly with increasing pyrolysis temperature, except for walnut shell. Total concentrations of P, Ca, K, Na, Fe, Zn, Cu, and Mn and available concentrations of K, Ca, Mg, and P increased with pyrolysis temperature increasing in all samples, except at walnut shell-derived biochar. According to CHN analysis, by increasing pyrolysis temperature, the total carbon concentration increased but total nitrogen and hydrogen concentrations decreased. The pH value decreased with time until 72 hours, beyond which a near steady-state condition was attained. Relationships between pH and CaCO₃-eq content of biochars were close and linear. The FT-IR spectra showed that aromatic C increased by increment in heating. Also, by increasing pyrolysis temperature, the mean pore diameter decreased but micropores volume increased and led to increase in the specific surface area of biochars. The results of this study suggest that biochars produced at 300 and 400˚C may have potential as fertilizer in calcareous soils because of low pH and EC, with high mass yield.
 

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This study aimed to assess the effect of incubation time and sewage sludge on peppermint biomass, essential oil yield, and Zinc (Zn), lead (Pb), and Cadmium (Cd) concentrations in the plant tissues as well as assessing phytoremediation potential of peppermint grown in contaminated calcareous soils. A greenhouse experiment was conducted by growing peppermint (Mentha pipertia L.) in two contaminated soils treated with three levels of sewage sludge (0, 10, and 30 g kg^-1) over two incubation times (30 and 120 days). Results revealed an increase in plant biomass and essential oil yield with an increase in incubation time and the sewage sludge amount. The concentrations of Zn, Pb, and Cd in plant tissues increased significantly in all treatments, except Cd concentration in plants growing on 10 g kg^-1 of sewage sludge and incubated for 120 days. No traces of Zn, Pb, and Cd were found in essential oil of plants treated with 10 g kg^-1 of sewage sludge. In other treatments, the concentrations of these metals in the essential oil were found within the limits recommended for medicinal plants. Unlike the bioaccumulation factor, the translocation factor of the studied metals decreased with an increase in the sewage sludge amount and incubation time. Although peppermint was not a sustainable plant to lower the pollution load, as the biomass production increased significantly and metals concentrations in essential oil remained within the recommended limits in all treatments, it can be concluded that peppermint can be used for cultivation in contaminated soils treated with sewage sludge.

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Original Walkley-Black (OWB) method has been extensively used for measuring Soil Organic Carbon (SOC), mainly because of its convenience. However, the reliability of this method is still under speculation. In recent years, Permanganate Oxidizable Carbon (POXC) has been suggested to be more useful than the total SOC. In the present study, SOC contents of the 20 non-calcareous soil samples (0-20 cm) were determined by the OWB method and its modified versions (WB with external heating and WB using colorimetric determination) to understand their relationships with easy-to-find Soil Organic Matter (SOM) determined by the method of Loss-On-Ignition (LOI) at two temperatures (400 and 550°C). The POXC was also determined in the sampled soils and applicable relationships were specified between these methods. Eight of the 20 soils were selected to determine the accuracy of different WB methods using total organic carbon by CHN elemental analysis. Results showed strong power relationships between LOI and OWB methods. The WB method with external heating exhibited the highest recovery (95.3%) among the tested methods. This could be attributed to the finer soil particles used in the proposed method (less than 0.15 mm) than what has been used in the conventional method (less than 0.5 mm). The POXC method showed a high correlation with OWB method and, on average, accounted for only 4.1% of the Total Organic Carbon (TOC). This would likely reduce the value of POXC as an independent parameter to derive the labile fraction of SOC.