High-efficiency extraction of bromocresol purple dye and heavy metals as chromium from industrial effluent by adsorption onto a modified surface of zeolite: Kinetics and equilibrium study

Abstract

Tannery industrial effluent is rich in heavy metals and basic dyes as bromocresol purple (BCP), poses an economic problem and a serious danger to the environment. This research had evaluated the importance of the adsorption properties of a modified clinoptilolite (CL) (a type of zeolite) for the removal of BCP dye and some heavy metals as total chromium (tCr) in the ammoniac phase. The modified adsorbent was prepared by mixing solid waste (SW) and CL in a ratio 10:1. The CL, SW, and CL-SW materials were characterized and the adsorption behavior of the later to BCP and tCr was completely studied. The batch removal showed the optimal conditions for BCP adsorption: pH (6.5), time (t) (60 min), temperature (T) (303.15 K), sorbent dosage (m) (60.4 mg), and initial concentration (Co) (11.7 mg/L). Moreover, the optimum conditions for tCr removal were: pH (8.8), t (55 min), T (303.15 K), m (400 mg), and Co (16.0 mg/L). Cr desorption mechanism was an ion exchange reaction. The experimental data of tCr were best fitted by the Freundlich isotherm and the pseudo-second-order kinetic model. The maximum adsorption capacities of BCP and tCr onto the CL-SW were 175.5 mg/g and 37 mg/g, respectively. Thermodynamic studies revealed that the adsorptions were spontaneous and endothermic with an increase of entropy. The CL modified adsorbent seems to be a good and efficient for the removal of dyes as BCP and such heavy metals including Cr. Surprisingly, this treatment has largely improved the physicochemical properties of the industrial wastewater and proved a new concept "Polluter Cleans Polluters (PoClPos)".