Vamvuka, et al (2024) Enhanced Adsorption of Arsenate from Contaminated Waters by Magnesium-, Zinc- or Calcium-Modified Biochar—Modeling and Mechanisms. C. https://doi.org/10.3390/c10030061

Arsenic contamination in water is a significant environmental and public health concern due to its toxic and carcinogenic properties. It can enter water systems through both natural sources and human activities like mining and industrial processes. Given its severe health implications, the World Health Organization has set a maximum allowable arsenic limit in drinking water at 10 µg/L. Various technologies exist to remove arsenic from water, but adsorption is often preferred for its cost-effectiveness and ease of operation. Traditional activated carbonActivated carbon is a form of carbon that has been processed to create a vast network of tiny pores, increasing its surface area significantly. This extensive surface area makes activated carbon exceptionally effective at trapping and holding impurities, like a molecular sponge. It is commonly More, while effective, is expensive and challenging to dispose of, leading researchers to explore alternative adsorbents like biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More.

Biochar, a product of biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, is gaining attention for its potential in water treatment due to its low production cost and favorable properties such as high carbon content and stability. However, the negatively charged surface of biochar limits its capacity to adsorb anionic pollutants like arsenate (As5+). This study investigates how modifying biochar with magnesium (Mg), zinc (Zn), or calcium (Ca) can enhance its arsenate adsorption capabilities.

The raw material used in this research was almond shell biochar, which was physically activated by nitrogen and steam. For the modifications, almond shell biochar was treated with MgCl2.6H2O, Zn(NO3)2.4H2O, and quarry dust to create Mg-, Zn-, and Ca-modified biochar. These modifications aimed to improve the biochar’s physicochemical properties to better adsorb As5+ ions from aqueous solutions.

The study examined various factors affecting arsenate adsorption, including contact time, adsorbent dose, initial arsenate concentration, and solution pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More. Kinetic experiments revealed that arsenate adsorption by non-modified almond shell biochar reached equilibrium in about 12 hours, achieving a maximum removal efficiency of 29.4% at an initial concentration of 10 mg/L. This performance significantly improved with modified biochars, particularly with Zn-modified biochar, which showed excellent adsorption efficiency across both low and high arsenate concentrations.

The adsorption mechanisms were explored through structural analyses and isotherm modeling. The Freundlich isotherm model, which suggests multilayer adsorption on heterogeneous surfaces, best described the experimental data. For non-modified biochar, the maximum adsorption capacity was 12.4 mg/g. This capacity increased substantially for Mg-, Zn-, and Ca-modified biochars, with values of 21.5 mg/g, 24.3 mg/g, and 24.3 mg/g, respectively. When the adsorbent dose was reduced to 2 g/L, these capacities further increased to 35 mg/g, 50 mg/g, and 49 mg/g, respectively.

FTIR spectra indicated the presence of various functional groups on the biochar surface before and after arsenate adsorption. Peaks corresponding to As-O and As-OH bonds confirmed the adsorption of arsenate on the biochar. The disappearance of Mg-O peaks and the formation of new peaks suggested that chemical interactions between arsenate ions and the biochar’s functional groups were crucial to the adsorption process. Additionally, XRD analysis identified new crystalline phases after arsenate adsorption, supporting the occurrence of surface precipitation as another key adsorption mechanism.

The study’s findings highlight the potential of modified biochars as efficient adsorbents for arsenate removal from contaminated water. By enhancing the adsorption capacity and efficiency through simple modifications, these materials can provide a cost-effective and sustainable solution for addressing arsenic contamination. This approach not only leverages waste materials like almond shells but also offers a viable alternative to traditional activated carbon, contributing to environmental sustainability and public health protection.