[Effects of pH and coexisting cations on ammonia adsorption from aqueous solution by strawberry stem powder]

Batch equilibrium experiments were carried out to study ammonia adsorptions from aqueous solution by strawberry (Fragaia ananassa Duchesne) stem powder. The effects of pH, coexisting cations, initial ammonia concentration and temperature were investigated as well. The results showed that the equilibrium data fitted well to the Langmuir model and Freundlich model, and the maximum adsorption capacities were 3.05, 4.24 and 4.79 mg x g(-1) at 15, 25 and 35 degrees C respectively. The increase of temperature was favorable to ammonia adsorption. The optimal pH of ammonia adsorption was in the range of 4-8. The NH4+ content decreased at higher pH and the negative charges decreased at lower pH, resulting in the decrease of ammonia adsorption at both higher and lower pH. The pH changes after adsorption buffered both effects. K+, Na+, Ca2+ and Mg2+ had no effect on ammonia adsorption by strawberry stem, but Zn2+ and Al3+ decreased the adsorption for their hydrolyzation. The ammonia adsorption by strawberry stem powder could be applied in a large pH range and could not be affected by usual metal cations in wastewater, therefore the strawberry stem powder not only could be a suitable ammonia adsorbent, but also had advantages comparing with most mineral materials.