Nitrates and phosphates, found in fertilizers, are the most common eutrophication-causing agents. Douglas fir biochar (BC), a syngas byproduct, was treated with different Al/Mg ratios of sulfate (5% w/w metal loading) followed by an NaOH treatment. The greatest phosphate uptake at 25 °C and pH 7 was attributed to the composite with a Mg/Al 2:1 ratio prepared at pH 13 (AMBC). Batch AMBC phosphate uptake was optimized for initial pH, equilibrium time, temperature, and initial phosphate concentration. Phosphate removal following pseudo-2nd-order kinetics and increases gradually before reaching a max at pH 11, with 95% phosphate uptake in 15 mins. The Sips isotherm model provided the best sorption data fit resulting in a 42.1 mg/g capacity at 25 °C and pH 11. Endothermic and spontaneous adsorption were determined using van ’t Hoff’s plots. BET, XRD, XPS, SEM, TEM, and EDS were used to characterize the biochar before and after phosphate sorption. Used AMBC has the potential to be exploited as a phosphate fertilizer as a key part of an environmentally friendly agricultural management plan.

Oil spills cause massive loss of aquatic life. Oil spill cleanup can be very expensive, have secondary environmental impacts, or be difficult to implement. This study employed five different adsorbents: (1) commercially available byproduct Douglas fir biochar (BC) (SA ∼ 695 m2/g, pore volume ∼ 0.26 cm3/g, and pore diameter ∼ 13-19.5 Å); (2) BC modified with lauric acid (LBC); (3) iron oxide-modified biochar (MBC); (4) LBC modified with iron oxide (LMBC); and (5) MBC modified with lauric acid (MLBC) for oil recovery. Transmission, engine, machine, and crude oils were used to simulate oil spills and perform adsorption experiments. All five adsorbents adsorbed large quantities of each oil in fresh and simulated seawater with only a slight pH dependence, fast kinetics (sorptive equilibrium reached before 15 min), and high regression fits to the pseudo-second-order kinetic model. The Sips isotherm model oil sorption capacities for these sorbents were in the range ∼3-11 g oil/1 g adsorbent. Lauric acid-decorated (60-2 wt %) biochars gave higher oil adsorption capacities than the undecorated biochar. Lauric acid enhances biochar hydrophobicity and its water contact angle and reduces water influx into biochar's porosity preventing it from sinking in water for 3 weeks. These features were observed even at 2% wt of lauric acid (sinks only after 2 weeks). Magnetization by magnetite nanoparticle deposition onto BC and LBC allows the recovery of the exhausted adsorbent by a magnetic field as an alternative to filtration. Oil sorption was endothermic. Recycling was demonstrated after toluene stripping. The oil-laden adsorbents' heating values were obtained, suggesting an alternative use of these spent adsorbents as a low-cost fuel after recovery, avoiding waste disposal costs. The initial and oil-laden adsorbents were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmet-Teller surface area, contact angle, thermogravimetric analyses, differential scanning calorimetry, vibrating sample magnetometry, elemental analysis, and X-ray photoelectron spectroscopy.