Ca-Mg modified attapulgite for phosphate removal and its potential as phosphate-based fertilizer

Near-complete recovery of phosphorus from fresh human urine: Combining magnesium-air fuel cells with modified granular attapulgite

In light of the urge demand for sustainable development and environmental protection, the recovery of phosphorus from source-separated urine holds great significance. This study proposed a novel approach combining magnesium-air fuel cells (MAFC) with modified granular attapulgite (GAT) to recover phosphorus from urine, producing a bulk blending fertilizer and soil amendment. The phosphorus adsorption capacity of GAT was enhanced by more than threefold following modification. The combined process attained a phosphorus recovery efficiency of 99.97 %, with the effluent phosphorus concentration decreased to 0.18 mg L-1, which complies with the discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002). In practical implementation, the process effectively treated real urine, yielding artificial phosphate ores (APOs) with a struvite content exceeding 88 % and a phosphate purity over 98 %. The pilot-scale assessment indicated a net benefit of 11.29 $·m-3 of urine, demonstrating significant economic feasibility. This work presents an innovative strategy for the efficient recovery of phosphorus from complex wastewater, showcasing its promising potential for practical applications.

Boosting the phosphate adsorption of calcite by low Mg2+-Doping

Calcite is a promising material choice for adsorbing phosphates because of its abundance and environmentally benign nature. However, the slow adsorption kinetics and hence low adsorption capacity within a short time frame hinders its practical application. In this work, we solve these problems by presenting a low Mg2+-doped calcite adsorbent, Mg-10. With a 3.75 wt% of Mg2+ doping, Mg-10 exhibits a remarkable adsorption capacity of 157.7 mg P/g. It also demonstrates a substantial boost in the adsorption kinetics, achieving a sixfold increase in adsorption capacity within 24 h compared to the undoped calcite. Meanwhile, Mg-10 not only offers improved adsorption selectivity but also maintains a stable effluent pH, underscoring its environmental compatibility. By conducting soil column experiments, we find that Mg-10 quickly captures the excess phosphates during the mimicking fertilization process, and slowly releases the nutrient afterwards, which can increase the feralization efficiency. These results provide alternative strategies for managing phosphate pollution originated from fertilization, and underscores the potential of Mg-10 in sustainable agriculture and environmental remediation.

Adsorption performance and mechanism of a starch-stabilized ferromanganese binary oxide for the removal of phosphate

Effective removal of phosphate from water is essential for preventing the eutrophication and worsening of water quality. This study aims to enhance phosphate removal by synthesizing starch-stabilized ferromanganese binary oxide (FMBO-S), discover the factors, and investigate adsorption mechanisms. FMBO and FMBO-S properties were studied using Scanning Electron Microscopy, BET analysis, Polydispersity Index (PDI), Fourier Transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). After starch loading, the average pore diameter increased from 14.89 Å to 25.16 Å, and significantly increased the pore volume in the mesopore region. FMBO-S showed a PDI value below 0.5 indicating homogeneous size dispersity and demonstrated faster and higher adsorption capacity: 61.24 mg g-1 > 28.57 mg g-1. Both FMBO and FMBO-S adsorption data fit well with the pseudo-second-order and Freundlich models, indicating a chemisorption and multilayered adsorption process. The phosphate adsorption by FMBO was pH-dependent, suggesting electrostatic attraction as the dominant mechanism. For the FMBO-S, phosphate adsorption was favored in a wide pH range, despite the weaker electrostatic attraction as evident from the point of zero charge and zeta potential values, indicating ligand exchange as a main mechanism. Moreover, the XPS analysis shows a significant change in the proportion of Fe species for FMBO-S than FMBO after phosphate adsorption, indicating significant involvement of Fe. Meanwhile, phosphate adsorption was almost unaffected by the presence of Cl-, NO3-, and SO42- anions, whereas CO32- significantly reduced the adsorption capacity. This study revealed that FMBO-S could be a promising, low-cost adsorbent for phosphate removal and recovery from water.