Rice Straw Biochar and Magnetic Rice Straw Biochar for Safranin O Adsorption from Aqueous Solution

This study investigates the adsorption of Safranin O (SO) from aqueous solution by both biochar and magnetic biochar derived from rice straw. Rice straw biochar (RSB) was made by pyrolysis in a furnace at 500 °C, using a heating rate of 10 °C·min−1 for 2 h in an oxygen-limited environment, whilst the magnetic rice straw biochar (MRSB) was produced via the chemical precipitation of Fe2+ and Fe3+. The physicochemical properties of the synthesized biochars were characterized using SEM, SEM- EDX, XRD, FTIR techniques, and N2 adsorption (77 K) and pHpzc measurements. Batch adsorption experiments were used to explore the effect of pH, biochar dosage, kinetics, and isotherms on the adsorption of SO. Experimental data of RSB and MRSB fit well into both Langmuir and Freundlich isotherm models, and were also well-explained by the Lagergren pseudo-second-order kinetic model. The maximum SO adsorption capacity of MRSB was found to be 41.59 mg/g, while for RSB the figure was 31.06 mg/g. The intra-particle diffusion model indicated that the intra-particle diffusion may not be the only rate-limiting step. The collective physical and chemical forces account for the adsorption mechanism of SO molecules by both RSB and MRSB adsorbents. The obtained results demonstrated that the magnetic biochar can partially enhance the SO adsorption capacity of its precursor biochar and also be easily separated from the solution by using an external magnet.

Effects of Modification and Co-Aging with Soils on Cd(II) Adsorption Behaviors and Quantitative Mechanisms by Biochar

In this study, original rice straw biochar and two KMnO4-modified biochars (pre- and postmodification) were prepared, which were all pyrolysed at 400℃. Premodified biochar had the largest Cd adsorption capacity, strongest acid and solute buffering capacity, which benefited from the increase of carbonate content, specific surface area and the emergence of Mn(II) and MnOx through modification. Original and premodified biochars were then conducted four types of aging process, namely, aging without soil, co-aging with acid (pH=5.00), neutral (pH=7.00) and alkaline (pH=8.30) soils, using an improved three-layer mesh method. The adsorption capacities of modified biochar were always larger than those of original biochar after aging processes. After four aging processes, Cd(II) adsorption capacities were basically in the order of aged biochar without soil > biochar co-aged with alkaline soil > biochar co-aged with neutral soil > biochar co-aged with acid soil, and KMnO4-modified biochar was always better than original biochar after co-aging with soils. The dominant adsorption mechanism of original and premodified biochars (fresh and aged) for Cd(II) was all the precipitation and adsorption with minerals (accounted for 58.55%~85.55%). In this study, we highlighted that biochar remediation for Cd should be evaluated by co-aging with soil instead of aging without soil participation.

Impact of Different Biochars on Microbial Community Structure in the Rhizospheric Soil of Rice Grown in Albic Soil

The purpose of this study was to clarify the effects of biochar on the diversity of bacteria and fungi in the rice root zone and to reveal the changes in soil microbial community structure in the root zone after biochar application to provide a scientific basis for the improvement of albic soil. Rice and corn stalk biochar were mixed with albic soil in a pot experiment. Soil samples were collected at the rice maturity stage, soil nutrients were determined, and genomic DNA was extracted. The library was established using polymerase chain reaction (PCR) amplification. The abundance, diversity index, and community structure of the soil bacterial 16SrRNA gene V3 + V4 region and the fungal internal transcribed spacer-1 (ITS1) region were analyzed using Illumina second-generation high-throughput sequencing technology on the MiSeq platform with related bioinformatics. The results revealed that the biochar increased the soil nutrient content of albic soil. The bacteria ACE indexes of treatments of rice straw biochar (SD) and corn straw biochar (SY) were increased by 3.10% and 2.06%, respectively, and the fungi ACE and Chao indices of SD were increased by 7.86% and 14.16%, respectively, compared to conventional control treatment with no biochar (SBCK). The numbers of bacterial and fungal operational taxonomic units (OUT) in SD and SY were increased, respectively, compared to that of SBCK. The relationship between soil bacteria and fungi in the biochar-treated groups was stronger than that in the SBCK. The bacterial and fungal populations were correlated with soil nutrients, which suggested that the impacts of biochar on the soil bacteria and fungi community were indirectly driven by alternation of soil nutrient characteristics. The addition of two types of biochar altered the soil microbial community structure and the effect of rice straw biochar treatment on SD was more pronounced. This study aimed to provide a reference and basic understanding for albic soil improvement by biochar, with good application prospects.

Enhanced fluoride removal from drinking water in wide pH range using La/Fe/Al oxides loaded rice straw biochar

A novel and highly efficient adsorbent was prepared by loading La/Fe/Al oxides onto rice straw biochar (RSBC) and was tested for the ability to remove fluoride from drinking water. Characterized by SEM, XRD, Zetapotential and FTIR, it was found that the ternary metal oxides were successfully loaded on the surface of biochar in amorphous form, resulting in the formation of hydroxyl active adsorption sites and positive charges, which played a synergistic role in fluoride removal. Through batch adsorption tests, key factors including contact time, initial fluoride concentration, initial pH and co-existing anions effects were investigated. Results showed that the tri-metallic modified biochar (La/Fe/Al-RSBC) had excellent fluoride removal performance with an adsorption capacity of 111.11 mg/g. Solution pH had little impacts on the removal of fluoride, the adsorbent retained excellent fluoride removal capacity in a wide pH range of 3.0–11.0. The co-existing anions had almost no effect on the fluoride removal by La/Fe/Al-RSBC. In addition, La/Fe/Al-RSBC could be regenerated and reused. Electrostatic adsorption and ion exchange were responsible for this adsorption behavior. These findings suggested the broad application prospect of a prepared biochar adsorbent based on rare earth and aluminum impregnation for the fluoride removal from drinking water.