25 ml of urine solutions with different initial concentrations of
urea (25%: 4950 mg L1, 50%: 9900 mg L1, 75%: 14,850 mg L1
and 100%: 19,800 mg L1) were prepared in Erlenmeyer flasks
(250 ml). 1–3 g of MACCS powder was added to 25 ml of urine
solutions, and kept in an incubator shaker, where shaking speed
(125–200 rpm) and time (0–360 min) were varied continuously.
The flasks were then removed from the shaker and sample was
withdrawn to be analyzed using a UV–visible spectrophotometer
(Shimadzu UV-1601, Japan) at 430 nm [17]. The amount of urea
adsorbed at equilibrium, qe (mg g1), was calculated using Eq.