Production and characterization of porous magnetic biochar: before and after phosphate adsorption insights

Abstract

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.

A Review on Magnetic Nanobiochar with Their Use in Environmental Remediation and High-Value Applications

“…Magnetic Properties. Due to the presence of magnetic properties in the nanobiochar, it has an attractive saturationremanence value with better crystallinity [85]. It helps in the separation of contaminants from water and wastewater treatments with the help of magnetic forces so it is used in the extraction of spent gel beads which are used in the biodegradation of PAHs in marine water [58,86].…”

Iron and Magnesium Impregnation of Avocado Seed Biochar for Aqueous Phosphate Removal

“…High and low metal loadings (relative term) were based on the mass ratio of biochar to metal salt at 1:8 for high loading and 1:2 for low loading. These comparatively high metal loadings were chosen based on previous studies to ensure the metal impregnation of the AB [16,[25][26][27]. For Fe-loaded AB preparation, Fe (III) chloride hexahydrate (FeCl3•6H2O) and Fe (II) chloride tetrahydrate (FeCl2•4H2O) were dissolved in DI water in 1:1 ratio, and AB was added to the Fe chloride solution similarly to the method of a previous study [28].…”

“…where KF is the Freundlich affinity coefficient ([mg g −1 ]/[mg L −1 ] −1/n ), n is the Freundlich linearity constant, and 1/n indicates the surface heterogeneity [27,31]. These parameters were determined using the linearized form of the Freundlich equation:…”

“…The Smax values of Mg-loaded AB were 30 mg g −1 for AB + High Mg and 40 mg g −1 for AB + Low Mg, but the validity of Smax values was questionable due to the poor fitting of measured data with the Langmuir model. Note that the Langmuir model assumes that adsorption occurs on a finite number of adsorption sites (monolayer coverage), allowing the estimation of Smax [27,30]. The Freundlich model is applicable for adsorption onto heterogenous surfaces with multiple stacking of adsorbates (multiple layer coverage), and the adsorption Phosphate adsorption (%)…”

“…The distinct presence of Mg(OH)2 granules in Mg-loaded AB (Figure 2) may explain the heterogenous nature of the surface and the better fitting with the Freundlich model. Note that the 1/n value from the Freundlich model indicates the surface heterogeneity of an adsorbent [27]. Mg-loaded AB (0.64-0.78) had more than two-times greater 1/n values than those of Fe-loaded AB (0.31-0.33), indicating the heterogeneous nature of surface adsorption sites in Mg-loaded AB.…”