Using various biochars to remove heavy metals (HMs) from aqueous solutions has been increased in recent years. It is believed that the use of nanocompounds in biochars surface structure may increase the efficiency of contaminants removal. Therefore, this research tries to investigate the efficiency of walnut-shell biochar (WSB) alone or supported by nanoscale zero-valent iron (WSB-nZVI) on cadmium (Cd) removal in aqueous solution controlled by four variables including initial Cd concentration, initial solution pH, contact time, and adsorbent dosage by Box Behnken design under response surface methodology. The results of present study showed that WSB-nZVI has a significant priority on WSB of Cd removal efficiency in aqueous solutions. The existence of functional groups on the surface of WSB via precipitation and adsorption processes, as well as nZVI formed on the WSB-nZVI via generating adsorption and complexation processes, have increased the ability Cd removal than WSB raw adsorbent. The maximum predicted Cd removal efficiency based on the proposed model was 99.72% with desirability of 1, in initial Cd concentration of 70.78 mg L-1, pH of 6.92, adsorbent dose of 0.56 g L-1 and contact time of 40.42 min. پرونده مقاله

   Chemical stabilization of heavy metals is one of the soil remediation methods based on the application amendments to reduce mobility of heavy metals. A laboratory study was conducted to investigate the influence of different kinds of amendments on cadmium (Cd) stabilization in a Cd-spiked soil. The amendments were municipal solid waste compost (MSWC), Coal fly ash (CFA), rice husk biochars prepared at 300°C (B300) and 600°C (B600), zero valent iron (Fe0) and zero valent manganese (Mn0). The Cd-spiked soils were separately incubated with selected amendments at the rates of 2 and 5% (W/W) for 90 days at 25 °C. Soil samples were extracted by EDTA for periods of 5 to 975min. In addition, sequential extraction was used as a suitable method for identification of chemical forms of Cd and their plant availability. The addition of amendments to soil had significant effects on desorption and chemical forms of Cd. Changes in Cd fractions and their conversion into less soluble forms were clear in all treated soils. The addition of amendments resulted in a signiï‌cant reduction in mobility factor of Cd compared to the control treatment. Among all amendments tested, Fe0 was the most effective treatment in decreasing dynamic of Cd. Biphasic pattern of Cd desorption kinetic was fitted well by the model of two ï‌rst-order reactions. In general, from the practical point of view, Fe0, MSWC and Mn0 treatments are effective in Cd immobilization, while application of  Fe0 at 5% (W/W) was the best treatment for stabilization of Cd.  پرونده مقاله