Comparison study of phosphorus adsorption on different waste solids:Fly ash,red mud and ferric–alum water treatment residues

The adsorption of phosphorus （P） onto three industrial solid wastes （fiy ash, red mud and ferric-alum water treatment residual （FAR）） and their modified materials was studied systematically ufa batch experiments. Compared with two natural adsorbents （zeolite and diatomite）, three solid wastes possessed a higher adsorption capacity for P because of the higher Fe, A1 and Ca contents. After modification （i.e., the fly ash and red mud modified by FeC13 and FARs modified by HC1）, the adsorption capacity increased, especially for the modified red mud, where more Fe bonded P was observed. The P adsorption kinetics can be satisfactorily fitted using the pseudo-second-order model. The Langmuir model can describe well the P adsorption on all of the samples in our study, pH and dissolved organic matter （DOM） are two important factors for P adsorption. Under neutral conditions, the maximum adsorption amount on the modified materials was observed. With the deviation from pH 7, the adsorption amount decreased, which resulted from the change of P species in water and surface charges of the adsorbents. The DOM in water can promote P adsorption, which may be due to the promotion effects of humic-Fe（A1） complexes and the pH buffer function exceeds the depression of competitive adsorption.

Removing phosphorus from aqueous solutions by using iron- modified corn straw biochar

Iron-modified corn straw biochar was used as an adsorbent to remove phosphorus from agricultural runoff. When agricultural runoffs with a total phosphorus （TP） concentration of 1.86 mg.L-1 to 2.47 mg.L-1 were filtered at a hydraulic retention time of 2 h through a filtration column packed with the modified biochar, a TP removal efficiency of over 99% and an effluent TP concentration of less than 0.02mg.L-1 were achieved. The isotherms of the phosphorus adsorption by the modified biochar fitted the Freundlich equation better than the Langmuir equation. The mechanism of the phosphorus adsorbed by the modified biochar was analyzed by using various technologies, i.e. scanning electron microscopy （SEM）, X-ray diffraction （XRD） analysis, X-ray photoelectron spectroscopy （XPS）, and Fourier transform infrared spectroscopy （FTIR）. The results indicated that the surface of the modified biochar was covered by small iron granules, which were identified as Fe304. The results also showed that new iron oxides were formed on the surface of the modified biochar after the adsorption of phosphorus. Moreover, new bonds of Fe- O-P and P-C were found, which suggested that the new iron oxides tend to be Fe5（PO4）4（OH）3. Aside from removing phosphorus, adding the modified biochar into soil also improved soil productivity. When the modified biochar-to-soil rate was 5%, the stem, root, and bean of broad bean plants demonstrated increased growth rates of 91%, 64%, and 165%, respectively.