Phosphorus recovery from aqueous solutions using Bioclastic Granules (Lithothamnium calcareum).

Against the growing world demand for food and the possibility of recovering some nutrients, this work focused on the evaluation of the use of Bioclastic Granules (BG) from the algae Lithothamnium calcareum as sorbent material for the removal/recovery of phosphorus from aqueous solutions. The main variables that affect the sorption process, pH, initial concentration of phosphate, and GB, as well as the contact time, were evaluated. The effect of pH was very significant, obtaining the best results of PO43- removal at pH 5. In the coarser granulometric fractions (+ 106 - 150 and + 210 - 300 µm), the best removals were observed (around 75%). Regarding the initial PO43- concentration in the solutions, the highest removal (in the range of 74 to 78%) was observed in the lowest concentrations (5 to 70 mg L-1) and the best uptake (10 to 14 mg g-1) at higher concentrations (200 to 420 mg L-1). The PO43- sorption data fitted the Freundlich model well, with kF of 1.35 L mg-1 and n of 2.43. A qmax of 14.35 mg g-1 was obtained using the Langmuir model. Regarding the sorption data over time, a better fit to the pseudo-first-order kinetic model was observed, obtaining a calculated qeq of 6.56 mg g-1 and a k1 of 0.0073 min-1. The incorporation of PO43- ions in the GB structure was confirmed through the characterization results before and after the sorption experiments using X-ray fluorescence (FRX) and scanning electron microscopy (SEM) techniques.

Cadmium removal by bioclastic granules (Lithothamnium calcareum): batch and fixed-bed column systems sorption studies.

The potential of Bioclastic Granules - BG (calcium-carbonate-based material) using the algae Lithothamnium calcareum as sorbent for the removal of Cd(II) from aqueous solutions by sorption was evaluated through batch and continuous systems tests using a fixed-bed column. Sorption process variables, in particular pH (2-7), particle size (<38-300 µm), initial BG concentration (0.1-1.0 g L-1), initial Cd(II) concentrations (5-400 mg L-1) and contact time (5-240 min), were evaluated. Adsorption isotherm profiles of Cd(II) per BG were similar to an L-type, or Langmuir type, with the adsorption forming a monolayer of approximately 0.61 µm, with a qmax of 188.74 mg g-1 and kL of 0.710 L mg-1. Thomas's model considers that sorption is not limited to a chemical reaction but is controlled by mass transfer at the interface. In the present study, the obtained value of kTh was 0.895 mL h-1 mg-1, reaching a sorption capacity qo of 124.4 mg g-1. For the Yoon-Nelson model, it was possible to obtain two important parameters to describe the behavior of the column, the rate constant (kYN), obtaining a value of 0.09 h-1 and an τ of 82.12 h corresponding to the time required for sorption to occur of 50% of the solute in the rupture curve. X-ray diffraction and scanning electron microscopy analyses coupled to the X-ray dispersive energy system (SEM/EDS) of the BG after the Cd(II) ion sorption tests evidenced the formation of crystals with the prevalence of a new mineral phase (otavite).