Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides

• Published in: Journal of colloid and interface science Vol. 290; no. 1; pp. 45 - 51
• Main Authors: Chitrakar, Ramesh, Tezuka, Satoko, Sonoda, Akinari, Sakane, Kohji, Ooi, Kenta, Hirotsu, Takahiro
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.10.2005; Elsevier
• Subjects: Adsorption; Calcined layered double hydroxides; Chemistry; Exact sciences and technology; General and physical chemistry; Hot Temperature; Hydrogen-Ion Concentration; Hydroxides - chemistry; Magnesium - chemistry; Manganese - chemistry; Phosphate; Phosphates - chemistry; Seawater; Seawater - chemistry; Selectivity; Sodium Chloride - chemistry; Solid-liquid interface; Surface physical chemistry; Surface Properties; Calcined layered double hydroxides; Selectivity; Adsorption; Phosphate; Seawater; Phosphates; Hydroxides; Lamellar compound; Transition metal Compounds; Magnesium Hydroxides; Manganese Hydroxides
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2005.04.025

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 °C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm 3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide ( δ-MnO 2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm 3. The analyses of the uptakes of other constituents (Na +, K +, Ca 2+, Cl −, and SO 2− 4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of log K F = 1.25 and 1 / n = 0.65 , indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO 2− 4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm 3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.