Experimental and modeling investigations of ball-milled biochar for the removal of aqueous methylene blue

Novel adsorbents were produced through the grinding of biochars of different feedstock and pyrolysis temperature in a planetary ball mill. The removal effectiveness and mechanisms of aqueous methylene blue by these adsorbents were examined. Ball milled sugarcane bagasse biomass pyrolyzed at 450 degrees C (BMBG450) had the highest methylene blue sorption capacity thus was chosen for further study. Compared to unmilled bagasse biochar (BG450), BMBG450 had greater specific surface area, larger pore volume, smaller hydrodynamic radius, stronger negative zeta potential (about 1.6-fold increase), and more oxygen-containing functional groups (1.05 mmol/g increase). These characteristics resulted in much greater methylene blue removal capacity (354 mg/g Langmuir maximum adsorption capacity vs. 17.2 mg/g of original BG450). The increased in BM-biochar's external and internal surface areas exposed its graphitic structure and oxygen-containing functional groups, thus enhancing methylene blue adsorption via p-p interaction and electrostatic attraction. Experimental and modeling results suggest external mass transfer as the rate-limiting adsorption step for BG450 and surface diffusion as the rate-limiting adsorption step for BMBG450. BM-biochars had a lower equilibrium dosage and shorter reactor detention time when applied in a completely mixed flow reactor (CMFR).

通过在行星式球磨机中研磨不同原料和热解温度的生物炭制备了新型吸附剂。研究了这些吸附剂对水溶液中亚甲基蓝的去除效果和机制。在450℃下热解并经球磨的甘蔗渣生物质（BMBG450）具有最高的亚甲基蓝吸附能力，因此被选作进一步研究。与未研磨的甘蔗渣生物炭（BG450）相比，BMBG450具有更大的比表面积、更大的孔体积、更小的流体动力学半径、更强的负ζ电位（约增加1.6倍）以及更多的含氧官能团（增加1.05 mmol/g）。这些特性使得其对亚甲基蓝的去除能力大大提高（朗缪尔最大吸附量为354 mg/g，而原始的BG450为17.2 mg/g）。球磨生物炭外部和内部表面积的增加使其石墨结构和含氧官能团暴露出来，从而通过π - π相互作用和静电吸引增强了对亚甲基蓝的吸附。实验和模拟结果表明，对于BG450，外部传质是吸附的限速步骤，而对于BMBG450，表面扩散是吸附的限速步骤。当应用于完全混合流反应器（CMFR）时，球磨生物炭具有更低的平衡剂量和更短的反应器停留时间。