No abstract

Mg/Al ratio plays a significant role for anion adsorption by Mg/Al-layered double hydroxides (Mg/Al-LDHs) modified biochar. In this study, Mg/Al-LDHs biochar with different Mg/Al ratios (2, 3, 4) were prepared by co-precipitation for phosphate removal from aqueous solution. Factors on phosphate adsorption including Mg/Al ratio, pH, and the presence of other inorganic anions were investigated through batch experiments. Increasing Mg/Al ratio in the Mg/Al-LDHs biochar composites generally enhanced phosphate adsorption with Langmuir adsorption maximum calculated at 81.83mg phosphorous (P) per gram of 4:1Mg/Al-LDHs biochar at pH3.0. The adsorption process was best described by the pseudo-second-order kinetic model. Solution pH had greater effects on the phosphate adsorption by Mg/Al LDHs biochar composites with lower Mg/Al ratios. The presence of other inorganic anions decreased the phosphate adsorption efficiency in the order of F(-) > SO4(2-) > NO2(-) >Cl(-). Phosphate adsorption mechanism involves ion exchange, electrostatic attraction and surface inner-sphere complex formation. Overall, Mg/Al-LDHs biochar composites offer a potential alternative of carbon-based adsorbent for phosphate removal from aqueous solution.

The present study deals with the preparation of a novel MgO-impregnated magnetic biochar (MMSB) for phosphate recovery from aqueous solution. The MMSB was evaluated against sugarcane harvest residue biochar (SB) and magnetic biochar without Mg (MSB). The results showed that increasing Mg content in MMSB greatly improved the phosphate adsorption compared to SB and MSB, with 20% Mg-impregnated MMSB (20MMSB) recovering more than 99.5% phosphate from aqueous solution. Phosphate adsorption capacity of 20MMSB was 121.25mgP/g at pH 4 and only 37.53% of recovered phosphate was desorbed by 0.01mol/L HCl solutions. XRD and FTIR analysis showed that phosphate sorption mechanisms involved predominately with surface electrostatic attraction and precipitation with impregnated MgO and surface inner-sphere complexation with Fe oxide. The 20MMSB exhibited both maximum phosphate sorption and strong magnetic separation ability. Overall, phosphate-loaded 20MMSB significantly enhanced plant growth and could be used as a potential substitute for phosphate-based fertilizer.

Metal oxide-biochar composites have been used for removing pollutants from aqueous systems. In this work, optimized MgO-impregnated porous biochar was prepared using an integrated adsorption-pyrolysis method for absorption of phosphate, ammonium and organic matter (humate). Results revealed that the MgO-biochar was comprised of nano-sized MgO flakes and nanotube-like porous carbon. Mg content had significant effects on the development of the nanotube-like porous carbon structure in MgO impregnated biochar and its adsorption capacity for phosphate, ammonium and humate. The adsorption isotherms fitted by Langmuir model illustrated that the optimized adsorbent, 20% Mg-biochar, exhibited maximum adsorption capabilities of more than 398 mg /g for phosphate, 22 mg/g for ammonium, and 247 mg/g for humate, respectively. The phosphate adsorption fitted the pseudo-second-order kinetic model, while ammonium and humate adsorption were best described by the intra-particle diffusion model. The existence of Cl − , NO 3 − , SO 4 2− , K + , Na + and Ca 2+ ions had no significant impacts on humate adsorption, but the presence of SO 4 2− and Ca 2+ affected the phosphate adsorption, and the presence of K + , Na + and Ca 2+ ions inhibited ammonium adsorption. Characterization of adsorbents by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) before and after treating swine wastewater revealed that struvite crystallization, electrostatic attraction, and π-π interactions contributed to the adsorption of phosphate, ammonium and humate. The results demonstrated that the optimized MgO-biochar could be employed as an effective adsorbent for the simultaneous removal and recovery of phosphate, ammonium and organic substances from nutrient-rich livestock wastewaters.

Saturated paste (SP) and 1:1 soil/water extractions (1:1) are commonly used to assess soil salinity for field remediation. Correlation of electrical conductivity (EC) and other analytes between the SP and 1:1 extraction methods have been documented, except the relationships were based on limited soil types and require further examination to be adequately evaluated. This study examined these relationships using 170 soils from petroleum and agriculture production sites. Saturated pastes and 1:1 extracts were prepared and analyzed for EC, major cations (Na+, K+, Mg2+, Ca2+), and major anions Cl−, SO42− Relationships of all analytes were established between the two methods using linear regression. Saturated paste extract EC (ECSP) was highly correlated with that of 1:1 extract EC (EC1:1) (r2 = 0.85, P < 0.001). Significant relationships also existed (r2 > 0.73, P < 0.001) between different ions in SP and 1:1 extracts. An independent validation set of 22 soils showed that the slopes of the regressions between predicted EC, Na+, and Cl− of SP equivalents from 1:1 extract measurements and direct SP extract measurements were very close to 1.0 suggesting that the regressions developed can accurately assess soil salinity in salt affected soils using 1:1 extract analysis instead of using the more expensive and time‐consuming SP extraction.