Phosphorus Removal Using Lignite Fly Ash

Phosphorus (P) release to surface waters leads to serious pollution. The development of technology for P removal offers the opportunity for abatement of environmental hazards and recycling. Fly ash is widely available and a cheap adsorbent; its alkaline properties make it interesting for precipitation of phosphates. An attempt was made to study the P removal ability of lignite fly ash. In order to determine the phosphate removal capacity of fly ash and the effect of adsorbent quantity (5 and 10 g per 100 ml), temperature (28 and 50 degrees C), retention time (5 and 30 min) on P removal, sorption studies were conducted using phosphate solutions containing 20, 50, 100, 150, and 200 mg/lP. The results showed that the lignite fly ash was able to remove even 100% of 20 mg/l P at 10 g adsorbent with 30 min retention time at 28 degrees C. The P removal capacity decreased with increase in P concentration; the removal was 86.51% at 200 mg/l P. The adsorbent quantity significantly influenced the P removal; the average removal was 94.81% at 5 g and 97.5% at 10 g. The Langmuir adsorption maximum was the highest for 5 g of fly ash-30 min equilibrium at 28 degrees C (40.98 mg/kg). The adsorption maxima decreased with increase in temperature, however, the factor related to bonding energy has increased at 50 degrees C. Altogether the study revealed that the lignite fly ash could be successfully used for instantaneous P removal at ambient conditions; however, other parameters like solid-liquid ratio, maximum carrying capacity, etc. need to be yet optimized.