Values of ki and correlation coefficients are listed in Table 3,from which it can be seen that the kinetics of copper adsorption on the SHI-W and SHI-C samples followed this model with R2 values higher than 0.95,indicating that intraparticle diffusion was involved in the adsorption process.For these samples,it seems that physisorption played the main role in the adsorption mechanism.However,for the SHI-BTCA,the R2 values did not support the fact that the metal-adsorption data closely follow this model,suggesting that,in this case,the diffusion mechanism is not the main interaction,and the process was mainly controlled by chemisorption.Nevertheless,for the three selected materials and the entire concentration range studied ,it was noted that the adsorption process tends to be followed by two linear regions with non-zero intercepts: the initial curved portion of the plots indicated a boundary layer effect while the second linear portion is due to intraparticle diffusion.Indeed,the data did not pass through the origin,indicating that intraparticle diffusion was not the only rate-limiting mechanism and that some other interactions also played an important role.The calculated ki values for each initial concentration indicated that,when the metal concentration was augmented,the rate constant increased for all the tested samples.The values of C also increased with copper concentration.However,the analysis of the data indicated that deviations from Weber and Morris model mainly occurred at high initial metal concentrations.Similar interpretations on this were reported before.The Elovich model,inspired by Zeldowitsch’s model and developed for gaseous systems,helps to predict the mass and surface diffusion,activation and deactivation energy of a given system,pot drying determining the nature of adsorption on the heterogeneous surface of the adsorbent,whether chemisorption or not.
This model is expressed by Eq.where a and b are the initial rate and desorption constant,respectively,during any experiment.Fig.6 shows that,for the three selected samples,the metal adsorption also fitted the Elovich equation,suggesting a chemisorption mechanism such as surface complexation formation and that shives surfaces are energetically heterogeneous.Table 3 lists the kinetic constants.In particular,when the concentration increased,the b constant decreased for both SHI-C and SHI-BTCA samples,suggesting a decrease in the availability of adsorption sites for copper adsorption.The analysis of the data clearly indicated that the Elovich model gave the best fit for the experimental data obtained for the SHI-BTCA sample,confirming the involvement of the carboxylate groups in the adsorption mechanism.Nevertheless,the data were also well simulated by the Elovich model for SHI-W and SHI-C samples,indicating the mechanism was complicated with the presence of both chemisorption and physisorption.By applying the Lagergren,Ho and McKay,and Elovich models,it is assumed that the overall adsorption process rate is governed by the rate of binding,whereas when applying the Weber and Morris model,the rate of mass transport is expected to govern the overall process rate.The Boyd model is also an adsorption diffusion model used to predict the mechanistic steps involved in an adsorption process,i.e.,whether the rate of removal of the metal takes place via film diffusion or particle diffusion mechanism.If the plot is a straight line passing through the origin,then adsorption is governed by a particle diffusion mechanism,otherwise governed by film diffusion.An analysis of the literature shows that,in numerous works,film diffusion is the limiting step during the initial stages of the adsorption process followed by intraparticle diffusion when pollutant species reach the material surface.However,it is difficult to estimate appropriate values of Bt for the entire time scale,so the data should be carefully interpreted.The good correlation obtained between the experimental data and predicted curves proved the validity of the Boydmodel only for the SHI-W sample,with R2 values higher than 0.95.For the two other samples,the Boyd model did not adequately fit the data.In addition,as shown in Fig.7,the plots for the three materials did not pass through the origin,revealing that the film diffusion controls the process for the copper adsorption onto three samples.And the properties of AC are also affected by the type of activator, the ratio of added activator, activation temperature, activation time and so on. In consideration of activation difficulty, supply stability and the price of raw materials, AC can be prepared by a wide range of different raw materials.
The use of agriculture byproducts or lignocellulosic materials, such as rice husks and waste newspapers to produce AC has been widely studied. Kazemipour et al., respectively used some agricultural products such as almond, hazelnut, walnut, and apricot to prepare AC Hemp, which can grow quickly in various climates and has various applications is an good choice owing to low cost, economic, and environmental considerations. Hemp, an annual herbaceous plant, as a result of hemp fiber processing technology is rapidly expanding, is widely cultivated in China . However, compared to hemp seed can be refined into biological diesel and hemp bast can be applied in the clothing, respectively. The hemp stems are almost useless and often burned through post-harvest burning of cultivation fields, which not only wastes the resources, but also polluts the environment. Hemp stems are very rich in cellulose and lignin, and have natural nano pore structure. Accordingly, the utilization of hemp stems to produce AC reduce the cost, enhance economic efficiency and contribute to comprehensive utilization of agricultural wastes. There are two processes for the preparation of activated carbons, the so-called physical and chemical activation. The results show that chemical activation has the advantage of high effective and well-controlle porosity. In spite of all kinds of activating agents are used, KOH which can promote AC to produce more pore structure is one of the most widely applied. Rosas et al. adopted phosphoric acid activation to product AC from hemp. A.H. Basta et al. used 2-steps KOH activation to prepare AC from rice straw. However, straw-based material such as hemp stems often have high ash content compared with other agricultural wastes, which are not benefit for the preparation of super AC. As a consequence, preparation and characterization of high performance AC from straw material was studied by few researchers. Not to mention the preparation mechanisms of straws materials-derived AC were investigated. Only Ru Yang et al. investigated characterization of AC derived from biomass source hemp stem via N2, CO2 and H2 adsorption.
Anthropogenic activities, especially those of the industrial and mining sectors, have left considerable areas of heavy metal – contaminated areas worldwide. Due to their nonbiodegradable and persistent characteristics, HMs cause serious soil and water contamination and severe health hazards for living beings upon exposure. In Europe, potentially polluting activities have taken place at an estimated 2.8 million sites, and only 24% of the sites have been inventoried. Currently, only 28% of all registered sites have been investigated, which is a powerful precondition for deciding whether remediation is needed. The term soil remediation refers to actions that are undertaken to limit the extent of soil contamination near hazardous waste sites to prevent exposure to harmful chemicals to people and other life forms. Currently, there are many soil remediation techniques where the most appropriate method depends on the soil characteristics, contamination type, treatment depth and costs involved. As reported by Dhaliwal et al., among the different technologies that are used to ameliorate contaminated soils, phytoremediation is the cheapest and fastest technique to decontaminate soil with HMs. Moreover, phytoremediation has been shown to be a cost-effective and eco-friendly technology compared to physicochemical soil reclamation methods. Metal hyperaccumulator plants can accumulate large amounts of concentrated HMs in their biomass and remain healthy, which makes them suitable for the phytoremediation of HMs in contaminated soil. Among the promising species that have been used for remediating HM-contaminated soils, the use of industrial hemp has shown promising phytoremediation potential in terms of morphophysiological and metal accumulation responses, remediation capacity, trace element phytoextraction and the phytoremediation capability of wild weed. In addition, industrial hemp grows in different climates and produces high biomass yields, and its roots grow deep into the soil, which allows the plant to penetrate deep into the soil and increases the efficiency of removing widespread contamination. Linger et al. found that industrial hemp accumulates HMs in all of its plant parts and that the highest contaminant concentrations accumulate in the leaves. This finding emphasizes the importance of plant management, treatment and disposal of contaminated biomass to avoid secondary pollution, since the methods that are used to recover HMs from plant biomass and/or the safe disposal of harvested plants are still limited. The same study also suggested that in the future, more research must be conducted to provide technological improvements regarding the proper disposal of harvested contaminated biomass. Wu et al. indicate that industrial hemp has been extensively applied, with appropriate pretreatments and investigations, to fields including bioenergy, paper production and construction materials. According to Zhang et al., the postharvest management of plant biomass can be developed, which would include energy production, cannabis drying where the coupling of bioremediation techniques to bioenergy production yields far-reaching social and economic benefits.
Notwithstanding the fact that the phytoremediation of HMcontaminated soil is perceived as an eco-friendly technique, such phytoremediation activities might generate considerable environmental impacts, mainly due to the on-field activities, transportation and disposal or treatment of the biomass. To evaluate the environmental burdens of phytoremediation techniques, life cycle assessment represents a valuable methodology to analyze the in-depth impacts. Other studies have underlined the environmental implications of several bioremediation technologies. Witters et al.found that phytoremediation technologies do not have the energy-consuming and CO2- emitting drawbacks of conventional remediation activities that consist of soil excavation, chemical stabilization, incineration, vitrification and soil washing. Ali et al. also emphasize that conventional remediation technologies may lead to the alteration of soil properties and the disturbance of microflora. In another work, Vigil et al.argued that if the contaminated biomass was not valorized, then the sustainability of phytoremediation was questionable. An LCA methodology was also applied by Vocciante et al. to evaluate the environmental sustainability of phytoremediation technology. The results emphasized the importance of correctly managing the disposal of the contaminated biomass that was produced, where biomass incineration could be more onerous than direct land filling but would be viewed as a more sustainable choice if combined with energy production. Moreover, O’Connor et al. found that phytoremediation at a site was resilient when faced with moderate sea level rises and other hydroclimatic effects that were induced by climate change. Despite the aforementioned studies conducted on phytoremediation, there is a lack of knowledge on assessing the energy and environmental impacts of such remediation techniques. Although the technical issues and suitability of industrial hemp for phytoremediation have been deeply analyzed, less attention has been given to the energy and environmental aspects of the entire supply chain. Despite the growing interest in industrial hemp cultivation, which is also supported by national and European founding and regulations, this ’new crop’ suffers from current limitations, which start with the lack of knowledge of cultivation techniques, concerns by farmers about the legality of cultivation, and the scarcity of product processing plants, especially for the textile and fiber sectors, which limits its diffusion. Moreover, new studies are needed to overcome the current limitations related to the development of more sustainable industrial hemp supply chains. The aim of this study was to assess and evaluate the energy and environmental impacts of growing industrial hemp for the phytoremediation of HM-polluted soil. Additionally, the use of contaminated biomass as an energy resource in 4 different valorization scenarios was also analyzed. The three novel aspects of the performed analysis can be summarized as follows: i) to the authors’ knowledge, none of the previous LCA studies evaluated the energy and environmental impacts of industrial hemp at each phase of the cleanup process; ii) the energy and environmental benefits of phytoremediation were evaluated under 4 different industrial hemp biomass valorization scenarios, which included analyses of different products harvested and different subsystems, such as industrial hemp cultivation in HM-contaminated soils, with and without hemp seed processing, with and without anaerobic digestion of the contaminated products for electricity generation and biomass/digestate incineration in a biomass-fired power plant for electricity production; and iii) the work applied a broad approach in the analyses by including the entire supply chain of industrial hemp for phytoremediation in real sites that were contaminated by HMs.