Recovery of Ammonia from Biomass Waste by Adsorption on Magnesium Phosphate Derived from Magnesium Ammonium Phosphate

Abstract

Ammonia in animal wastes causes eutrophication of the soil when these wastes are used as liquid fertilizer. Accordingly, it is desirable to recover ammonia from these wastes. We investigate the following two methods for recovery of ammonia: (i) recovery of gaseous ammonia, which was generated by aeration of the ammonia gas, by adsorption on the magnesium phosphate adsorbent derived from magnesium ammonium phosphate (MAP); and (ii) recovery of aqueous ammonium ions by adsorption on the same adsorbent. The adsorbent was prepared by treatment of MAP at 378 K, and the XRD pattern of the adsorbent shows that MAP structure disappeared after the treatment. Gaseous ammonia and aqueous ammonium ions were adsorbed on the adsorbents, and the amounts of ammonium ions adsorbed were larger than that of gaseous ammonia. The adsorption isotherms of aqueous ammonium ions and gaseous ammonia exhibited Langmuir- and Henry-type characteristics, respectively, indicating different adsorption mechanism between aqueous ammonium ions and gaseous ammonia. It was found that MAP structure was re-formed in the presence of water after the aqueous ammonium ions adsorption, while the structure of the adsorbent had hardly changed after the gaseous ammonia adsorption. The low adsorption energy (–3.0 kJ/mol) of gaseous ammonia indicates that physical adsorption. Consequently, adsorption of aqueous ammonium ions is a suitable method for recovery large amounts of ammonia, and we demonstrate that large amounts of ammonium ions are recovered from cow urine after hydrothermal treatment of it.