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The modification process of biochars enables different advantages including enhanced adsorption properties for different pollutants. Herein, porous magnetic biochars (PMB) were successfully produced from softwood biomass through a two-step pyrolysis process together with FeCl3 modification. The effect of production temperature on adsorption was studied at 200 or 300 °C, followed by iron salt modification and subsequent pyrolysis at 600 or 800 °C. Biochars were characterized before and after phosphate adsorption via various characterization methods to acquire structural, elemental, and morphological properties of the adsorbent. The effects of phosphate concentration, contact time, and temperature on the adsorption process were examined in the batch mode. The characterization showed embedded iron oxide crystals of 23 nm within the biochar structure with a magnetic strength of 38.9 emu/g, which can assist the separation process of the powdered adsorbent from the aqueous medium. The surface area of the PMB was measured as 93 m2/g and 0.002 cm3/g pore volume. PMB showed complete removal (100%) of phosphate at the lower concentration (5 mg/l P). At higher concentration (25 mg/l P), the biochar prepared under 200/800 °C showed the highest removal (30%). The adsorption was enhanced with time (optimal 3 h) and temperature, which shows endothermic chemisorption following Langmuir isotherm and Pseudo-second order kinetic models. The desorption study suggested the slow release of phosphate from the spent adsorbent and potential reuse for soil enhancement. These results point towards the sustainable use of PMB as an effective and magnetically recyclable adsorbent for phosphate removal and reclaim.

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This study aimed to investigate the effect of different activations on the properties of bio-based activated carbons (BACs) for water treatment. BACs were produced via pyrolysis by the carbonization stage and were followed by four different activation procedures. Chemical activation included the introduction of metal oxides or alkali on the structure of the sawdust-derived BACs, resulting in iron-activated carbon (BAC-Fe), copper-activated carbon (BAC-Cu), and sodium-activated carbon (BAC-Na). The physical activation was conducted in a CO2 environment with the usage of two types of locally available biomasses, resulting in husk-activated carbon (HAC) and wood-activated carbon (WAC). Depending on the activation, BACs can be developed with high porosity, active sites, and different additional functionalities such as antimicrobial and magnetic. The adsorption of natural organic matter (NOM) with chemically activated BACs yielded high removal percentages (97, 87, and 80% for BAC-Fe, BAC-Cu, and BAC-Na, respectively). The physically activated BACs demonstrated high adsorption capacities for dye – 278 mg/g for WAC and 213 mg/g for HAC. This outlines a wide range of BAC production possibilities with advanced functionalities.

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