Investigating the efficiency of pistachio pulp biomass and the produced biochar at two different temperatures in removing cadmium from aqueous solution

Document Type : Research Paper


1 Department of Soil Science, Agriculture Faculty, Shahid Bahonar University of Kerman, Kerman, Iran

2 Department of soil science,agriculture faculty. shahid bahonar university of kerman


Considering the environmental problems caused by heavy metals in surface and underground water, surface adsorption can be considered as a promising alternative to reduce heavy metal ions in water resources. In this study, cadmium absorption by pistachio pulp biomass and their produced biochars at 300 and 500 0C in 1401-1402 at Shahid Bahonar University of Kerman was investigated. The properties of biomass and the produced biochars were determined. The effect of pH (2-7), contact time (5-1440 minutes) and different initial concentrations (200-10 mg L-1) on cadmium absorption was evaluated. In addition, pseudo-first-order and pseudo-second-order kinetic models as well as Freundlich and Langmuir isotherm models were evaluated. The obtained results showed that the percentage of carbon increased and the percentage of hydrogen, nitrogen and sulfur decreased with pyrolysis of pistachio pulp biomass. SEM images showed that the surface of biochar is more irregular and rough than the biomass. Also, the optimal pH was 5 and the solution reached equilibrium in 120 minutes. Adsorption of cadmium by adsorbents showed a better fit with pseudo-second-order kinetic model and Langmuir isothermal model. The maximum cadmium absorption capacity by pistachio pulp biomass, biochar 300 and biochar 500 was 40.5, 58.2 and 72.5 mg g-1, respectively. The results of this study showed that the amount of cadmium absorption increased with the increase of pyrolysis temperature and pistachio pulp biochar has a high capacity to adsorb cadmium from aqueous solution.


Main Subjects

Investigating the efficiency of pistachio pulp biomass and the produced biochar at two different temperatures in removing cadmium from aqueous solution




With the rapid development of industrial activities, a large volume of industrial wastewater contains heavy metals and is released into surface and underground waters, which has led to many environmental problems. Heavy metals are dangerous due to their non-biodegradability, continuous bioaccumulation, and high toxicity. Therefore, the removal of dangerous heavy metal ions from polluted water is necessary to improve the environment and human health. Recently, the use of plant residue modifiers and biochar has been considered an excellent method for remediating polluted water sources. Biochar is a carbon-rich material that is obtained during the pyrolysis process at temperatures of 300 to 700 °C from the thermal decomposition of organic materials under oxygen-limited conditions. The purpose of this research is to investigate the efficiency of pistachio pulp biomass and the produced biochar at two temperatures of 300 and 500 °C on the adsorption of cadmium from aqueous solutions. Also, factors affecting adsorption, such as pH and contact time on cadmium adsorption, kinetic models, and adsorption isotherms, were investigated. Finally, the effect of pyrolysis temperature on the structural and chemical characteristics of biochars was studied.

Methods and Materials

This study was conducted in 1401–1402 at the Shahid Bahonar University of Kerman. Pistachio pomace as biomass for biochar production was obtained from a pistachio processing terminal in Anar city, Kerman province. Biomass was subjected to slow pyrolysis in an electric furnace under conditions of oxygen limitation at temperatures of 300 and 500 °C with an increase rate of 5 degrees per minute for 3 hours. To determine the pH and EC of biomass and biochar, a ratio of 1:10 distilled water to the weight of dry matter was used. The total amount of carbon, hydrogen and nitrogen in the samples was determined using the CHN-Analyzer device. FTIR, SEM, and XRD devices were used to investigate the characteristics of biomass and biochar. Factors affecting adsorption, including pH, contact time, and the initial concentration of the solution, were investigated. Different pHs of 2–7 were evaluated over a period of 24 hours in order to determine the optimal pH. In order to determine the optimal contact time, the times from 5 to 1440 minutes at the optimal pH were investigated. Also, in order to determine the optimal concentration, concentrations of 10–200 mg L-1 during the contact time and the optimal pH were investigated. To investigate the adsorption kinetics, pseudo first-order and pseudo-second-order kinetic models and Langmuir and Freundlich isotherm models were used to describe the data on cadmium adsorption by adsorbents.

Results and Discussion

pH had a significant effect on the amount of Cd adsorption, and with the increase of pH from 2 to 7, the adsorption capacity of all adsorbents increased. The kinetics of Cd adsorption by adsorbents show that the adsorption consists of two fast and slow stages. In the first 60 minutes, the rate of Cd adsorption by the adsorbents was fast, and then the rate decreased until it reached equilibrium in 120 minutes. The maximum adsorption capacity (qm) for Cd ions on pistachio residues and biochar at 300 and 500 °C is 40.5, 58.14, and 72.46 mg g-1, respectively. According to the obtained results, pH = 5 and a contact time of 120 minutes were chosen as the optimal pH and contact time, respectively. In general, the results showed that the capacity of Cd adsorption by pistachio pomace biochar at 500°C was higher than that of biochar prepared at 300°C and pistachio pomace residues. The study of adsorption kinetic models showed that for all adsorbents, the pseudo-second-order model had a better fit than the pseudo-first-order kinetic model due to a higher correlation coefficient and less error. Also, the Cd adsorption process showed a better fit with the Langmuir model for all adsorbents.


In this study, pH = 5 was chosen as the optimal pH. Also, the results showed that the adsorption of Cd by pistachio pulp biomass, biochar 300, and biochar 500 reached equilibrium in 120 minutes. Also, the kinetic data of Cd adsorption by all adsorbents were in better agreement with the pseudo-second-order kinetic model. The Langmuir isothermal model showed a good fit with the Cd adsorption data, with a maximum adsorption value of 72 mg g-1 obtained by Biochar 500. The results of this research showed that the biochar produced at 500 °C has a higher ability to adsorb Cd compared to the biochar produced at 300 °C and the raw biomass.

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