Investigation of Phosphate Adsorption in Aqueous Solution Using Steel Slag and HCI Treated Steel Slag

The excess of phosphate (P04-
3
) concentration released in water bodies could cause
problem to the environment in the form of eutrophication. One of the methods of
phosphate removal is adsorption. The aim of this project was to study the adsorption
of phosphate using HCl treated and untreated steel slag.
HCl acid was used to treat the steel slag by bathing the slag with HCl acid for 24
hours. The treated and untreated steel slag were then used for batch adsorption
studies which included the effect of agitation rate (30-150 rpm), temperature (25-
9o•q, initial phosphate concentration (100-300ppm) and contact time (30-120 min)
on the phosphate uptake by the steel slag.
FESEM result showed a more porous surface and a reduction in Ca2
+ ions after HCl
treatment. The average particle size of the steel slag was 20 f.lm. HCl treated steel
slag gave lower adsorption performance than the untreated steel slag. The highest
phosphate uptake was achieved by untreated steel slag experiments were 65%
(150rpm) and 87.13% (9o•q. HCl treated steel slag gave only 34.77% and 74.55%
phosphate uptake for the previous conditions mentioned.
Langmuir and Freundlich isotherms were found to be favorable for the adsorption
process as the results displayed correlation coefficient of 0.998 for untreated slag
with Qm value of 125 mg/g and n value of0.875. Correlation coefficient value of the
HCl treated steel slag was 0.999 with Qm value of37 mg/g and n value of0.752. Both
steel slags followed the pseudo second order kinetics with highest correlation
coefficient achieved at 0.999 and 0.998 for untreated and treated slags respectively.