Abstract
Elevated or unnatural levels of arsenic (As) and phosphorus (P) concentrations in soils and waterbodies from anthropogenic sources can present significant hazards for both natural ecosystems and human food production. Effective, environmentally friendly, and inexpensive materials, such as biochar, are needed to reduce mobility and bioavailability of As and P. While biochar features several physicochemical properties that make it an ideal contaminant sorbent, certain modifications such as mineral-impregnation can improve sorption efficiencies for targeted compounds. Here, we conducted sorption experiments to investigate and quantify the potential utility of magnesium (Mg) for improving biochar sorption efficiency of P and As. We synthesized a Mg-modified walnut shells-derived biochar and characterized its ability to remove As and P from aqueous solutions, thereby mitigating losses of valuable P when needed while, at the same time, immobilizing hazardous As in ecosystems. SEM-EDX, FTIR and elemental analysis showed morphological and functional changes of biochar and the formation of new Mg-based composites (MgO, MgOHCl) responsible for improved sorption potential capacity by 10 times for As and 20 times for P. Sorption efficiency was attributed to improved AEC, higher SSA, chemical forms of sorbates and new sorption site formations. Synthetized Mg-composite/walnut shell-derived biochar also removed >90% of P from real samples of wastewater, indicating its potential suitability for contaminated waterbody remediation.
Highlights
Phosphorus (P) is crucial for crop growth, natural deposits of inorganic P are limited
We found negligible As and P anion sorption capacity of pure biochars in aqueous solutions [8,9]
The obtained results of ultimate and proximate analyses of the studied samples are listed in pHDW pHKCl electrical conductivity (EC) Anion exchange capacities (AEC) specific surface areas (SSA) (m2/g) C (%) H (%) N (%) Mg phenolic groups lactonic groups carboxylic groups
Summary
Phosphorus (P) is crucial for crop growth, natural deposits of inorganic P are limited. Widespread application of P fertilizers and subsequent agricultural runoff has contaminated surface waterbodies, promoting eutrophication [1]. Phosphate concentrations as low as 20 μg/L can permit rapid growth of algae alongside oxygen depletion. The resulting harmful algal blooms produce toxins that diminish water fauna and flora populations [2]. Soil and water resources commonly suffer As contamination from industrial activities, mining, smelting and intensive pesticide applications. The maximum As concentration allowed by the US EPA is 24 mg/kg for soil and 10 μg/L for drinking water [4]. Increased As concentrations in soil and water presents a significant hazard for flora, fauna, and human food production
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