The acidic extracts of P were prepared by suspending the SSA in
HCl acid solution with L/S ratios of 2.5 and 3 for 10 min. The solids
in the suspension were removed by
filtration (0.5 mm). The HCl
acid (37 wt%) was purchased from Sigma-Aldrich. Other L/S ratio
with different amount of water has been tested; however, it has
been observed that decreasing the amount of water led to a
difficult
filtration process for separating the extract solution from
the SSA acid suspension. The optimal condition for the acid
extraction step has been selected based on the maximum P
extraction as well as a facilitated
filtration of the suspension.
In other studies, H2SO4 acid was widely used in the acid
leaching process to extract P from the SSA [13,14,26]. But acid
digestion with H2SO4 led to CaSO4 precipitates that shall hamper
the reuse of the
filter cake in construction materials [27]. In the
present work, HCl acid was selected for acid leaching, Ca will be
extracted together with P and both Ca ions and Cl ions will take
part in the crystallization of CaClH2PO4H2O, which is the target
product in the present work.