Preparation of Lanthanum-Modified Tea Waste Biochar and Its Adsorption Performance on Fluoride in Water.

In this study, tea waste was used as a raw material, and TBC (tea waste biochar) was prepared by pyrolysis at 700 °C. La(NO3)3·6H2O was used as the modifier to optimize one-way modification; the orthogonal experiment was undertaken to determine the optimal preparation conditions; and La-TBC (lanthanum-modified biochar) was obtained. The key factors for the adsorption of fluoride by La-TBC were investigated by means of batch adsorption experiments, and kinetics and isothermal adsorption experiments were carried out on the adsorption of fluoride in geothermal hot spring water. The adsorption mechanism of fluoride by La-TBC was analyzed via characterization methods such as SEM-EDS (Scanning Electron Microscope and Energy Dispersive Spectrometer), BET (Brunauer-Emmett-Teller), FTIR (Fourier transform infrared), XRD (X-ray diffraction), and so on. The results show that La-TBC had the best adsorption effect on fluoride at pH 7. The process of adsorption of fluoride follows the pseudo-second-order kinetics and Langmuir isothermal model, and the maximum theoretical adsorption quantity was 47.47 mg/g at 80 °C, while the removal rate of fluoride from the actual geothermal hot spring water reached more than 95%. The adsorption process was dominated by the monolayer adsorption of chemicals, and the mechanisms mainly include pore filling, ion exchange, and electrostatic interaction.

Lanthanum-modified tobermorite synthesized from fly ash for efficient phosphate removal.

Phosphate removal from water by lanthanum-modified tobermorite synthesized from fly ash (LTFA) with different lanthanum concentrations was studied. LTFA samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Brunauer‒Emmett‒Teller specific surface area analysis. The results showed that the LTFA samples were mainly composed of mesoporous tobermorite-11 Å, and LTFA1 with a lanthanum concentration of 0.15 M had a high specific surface area (83.82 m2/g) and pore volume (0.6778 cm3/g). The phosphate adsorption capacities of LTFA samples were highest at pH 3 and gradually decreased with increasing pH. The phosphate adsorption kinetics data on LTFA samples were most accurately described by the Elovich model. The adsorption isotherms were in the strongest agreement with the Temkin model, and LTFA1 showed the highest phosphate adsorption capacity (282.51 mg P/g), which was higher than that of most other lanthanum-modified adsorbents. LTFA1 presented highly selective adsorption of phosphate with other coexisting ions (HCO3-, Cl-, SO42-, and NO3-). In addition, phosphate was adsorbed onto LTFA samples by forming inner-sphere phosphate complexes and amorphous lanthanum phosphate. This study provides technical support for development of efficient fly ash-based phosphate adsorbents.

Nano La(OH)3 modified lotus seedpod biochar: A novel solution for effective phosphorus removal from wastewater.

Effective removal of phosphorus from water is crucial for controlling eutrophication. Meanwhile, the post-disposal of wetland plants is also an urgent problem that needs to be solved. In this study, seedpods of the common wetland plant lotus were used as a new raw material to prepare biochar, which were further modified by loading nano La(OH)3 particles (LBC-La). The adsorption performance of the modified biochar for phosphate was evaluated through batch adsorption and column adsorption experiments. Adsorption performance of lotus seedpod biochar was significantly improved by La(OH)3 modification, with adsorption equilibrium time shortened from 24 to 4 h and a theoretical maximum adsorption capacity increased from 19.43 to 52.23 mg/g. Moreover, LBC-La maintained a removal rate above 99% for phosphate solutions with concentrations below 20 mg/L. The LBC-La exhibited strong anti-interference ability in pH (3-9) and coexisting ion experiments, with the removal ratio remaining above 99%. The characterization analysis indicated that the main mechanism is the formation of monodentate or bidentate lanthanum phosphate complexes through inner sphere complexation. Electrostatic adsorption and ligand exchange are also the mechanisms of LBC-La adsorption of phosphate. In the dynamic adsorption experiment of simulated wastewater treatment plant effluent, the breakthrough point of the adsorption column was 1620 min, reaching exhaustion point at 6480 min, with a theoretical phosphorus saturation adsorption capacity of 6050 mg/kg. The process was well described by the Thomas and Yoon-Nelson models, which indicated that this is a surface adsorption process, without the internal participation of the adsorbent.

Comparative study of sediment phosphorus immobilization via the addition of lanthanum-modified and thermal-modified drinking water treatment sludge.

Lanthanum-modified drinking water treatment sludge (DTSLa) and thermal-modified drinking water treatment sludge (TDTS) were prepared from drinking water treatment sludge(DTS). The adsorption properties of DTSLa and TDTS on phosphate in water and the effects on the controlled release and morphology of phosphorus in sediment at different dosages (0%, 2.5%, 5%) were discussed. Combining with SEM, BET, XRD, FTIR, and XPS characterization methods, the immobilization mechanism of DTSLa and TDTS on phosphorus in sediment was explored. The addition of TDTS can transform NH4Cl-P (loosely sorbed P), BD-P (bicarbonate-dithionite extractable P), and Org-P (organic P) into stable NaOH-rP (metal oxide-bound P) in sediment, and the conversion amount will increase with the increase of TDTS supplemental amount. DTSLa converted NH4Cl-P, BD-P, Org-P, and NaOH-rP to more stable HCl-P (calcium-bound P). At the same time, the content of WSP (water-soluble phosphorus) and olsen-P (NaHCO3 extractable P) in sediment can be reduced by the addition of DTSLa and TDTS, reducing the risk of the release of phosphorus from the sediment to the overlying water. In addition, phosphorus can be directly removed from the interstitial water by DTSLa and TDTS, so as to reduce the phosphorus concentration gradient between the overlying water and the interstitial water, thus inhibiting the release of phosphorus from interstitial water to overlying water. The results showed that DTSLa is better than TDTS in terms of its adsorption capacity and adsorption effect on endogenous phosphorus in water, so DTSLa is more suitable to be used as a sediment conditioner to control the phosphorus content in water and sediment.

In-situ modified biosynthetic crystals with lanthanum for fluoride removal based on microbially induced calcium precipitation: Characterization, kinetics, and mechanism.

In this research, in-situ modified biosynthetic crystals with lanthanum (BC-La) were synthesized based on anaerobic microbially induced calcium precipitation (MICP) and investigated its capacity for groundwater defluoridation under various operational conditions. The kinetic and thermodynamic models were simulated to explore the effect of the material on the removal of fluoride ion (F-) under various parameters (pH, initial concentration of F-, and temperature). BC-La had the maximum F- adsorption capacity of 10.92 mg g-1 and 96.66% removal efficiency. The pseudo-second-order kinetic model and Langmuir isotherm model were the best kinetic and isotherm models for F- removal from BC-La, which indicated that F- were mainly spontaneously removed through chemisorption and adsorption processes. The specific surface area was 54.26 m2 g-1 and the average pore size was 9.0670 nm. BC-La mainly contained LaCO3OH, LaPO4, CaCO3, Ca5 (PO4)3OH, and F- was mainly removed through ion exchange with the material surface. Moreover, OH-, PO43-, and CO32- significantly influenced the F- removal. This work suggested a novel method for in-situ modification of anaerobic biosynthetic crystals, which improved the defluoridation effect of traditional biosynthetic crystals, increased the stability of the BC-La and allowed to remove F- from groundwater consistently.

Utilization of coal fly ash waste for effective recapture of phosphorus from waters.

Reutilization of the waste by-products from industrial and agricultural activities is crucially important towards attainment of environmental sustainability and the 'circular economy'. In this study, we have developed and evaluated a sustainably-sourced adsorbent from coal fly ash, which was modified by a small amount of lanthanum (La-FA), for the recapture of phosphorous (P) from both synthetic and real natural waters. The prepared La-FA adsorbent possessed typical characteristic diffraction peaks similar to zeolite type Na-P1, and the BET surface area of La-FA was measured to be 10.9 times higher than that of the original FA. Investigation of P adsorption capability indicated that the maximum adsorption (10.8 mg P g-1) was 6.14 times higher than that (1.8 mg P g-1) of the original fly ash material. The ζ potentials measurement and P K-edge X-ray Absorption Near Edge Structure (XANES) spectra demonstrated that P was bonded on La-FA surfaces via an adsorption mechanism. After applying the proposed adsorbent to real lake water with La/P molar ratios in the range from 0.5:1 to 3:1, the La-FA adsorbent showed the highest phosphate removal ability with a La/P molar ratio 1:1, and the P adsorption was similar to that performance with the synthetic solution. Moreover, the La-FA absorbent produced a negligible effect on the concentrations of total dissolved nitrogen (TDN), NH4+-N and NO3--N in water. This study thus provides a potential material for effective P recapture and details of its operation.

Phosphate adsorption characteristics of La(OH)3-modified, canna-derived biochar.

La(OH)3-modified canna biochar (CBC-La) was prepared by a coprecipitation method (dipping method), and its phosphate adsorption characteristics were investigated. The results show that the pseudo-second-order kinetics and the Langmuir model can be used to describe the adsorption process with a high level of accuracy. Adsorption equilibrium could be reached at 8 h, at which point the maximum adsorption capacity was shown to be 37.37 mg/g. CBC-La has excellent phosphate adsorption capacity in the middle to low concentrations (≤50 mg/L), and its removal rate can exceed 99 %. CBC-La also has wide pH adaptability (3-9) and a strongly selective adsorption performance. Notably, it can still maintain a removal rate of over 99.8 % in the presence of certain anions (NO3-, HCO3-, and CO32-), and the presence of NH4+ has a synergistic effect on the adsorption process. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the main mechanisms of CBC-La phosphate adsorption are electrostatic adsorption, ion exchange, ligand exchange and inner sphere complexation.

Promoted catalytic hydrodechlorination for deep degradation of chlorophenols over Rh-La/SiO2 catalyst.

Deep degradation of chlorophenols (CPs) into safe and ecofriendly cyclohexanol during catalytic hydrodechlorination (HDC), shows important practical significance and attractive prospect in the treatment of wastewater containing chlorophenols. An efficient Rh-La/SiO2 catalyst was developed, by employing La as promoter. The presence of La in catalyst promoted catalytic performance of HDC significantly. Characterization results revealed that the interaction occurred between Rh and La in Rh-La/SiO2 catalyst. This interaction accompanied with the high dispersion and finely particle size of active Rh, and generation of abundant Rh sites neighboring La atom. Kinetic study illustrated that Rh-La(1:1)/SiO2 catalyst possessed the fastest kinetic constants, and minimized the apparent activation energies of 4-CP, phenol and cyclohexanone greatly. Complete degradation of 4-CP with a very high yield of cyclohexanol (> 98%) can be achieved at room temperature, making Rh-La(1:1)/SiO2 catalyst to be a promising candidate for deep degradation of CPs during HDC and other Rh catalyzed hydrogenation reactions.