Preparation of the biosorbent
The biosorbent was prepared from mature leaves of Neem tree.
Clean and dust free leaves were
first sun dried for 3–4 days and then
allowed to dry in an air oven at 60–70 C for a long time. The dry
leaves was then crushed into
fine powder, Neem leaf powder (NLP)
using a mechanical grinder. The powder was then sieved and
fractionated using a series of sieves and the 74–105 micron fractions
were selected. NLP contains various water soluble amino acids,
carbohydrates and pigments, which get dissolved during shaking in
batch process and may hamper in spectrophotometric detection of
fluoride ions. Therefore, NLP were washed with distilled water in a
glass vessel at room temperature for several times to remove all the
water soluble pigments and other materials. Initially the washings
were turbid, but after several washings, the washings became clear
and at this point washing was stopped. The washed powder was