Chromium sorption on synthetic and natural rock minerals with emphasis on speciation behavior and kinetic model using Cr51

The presence of chromate in the aquatic environment poses toxicity and pollution to the environment. Therefore, the needs to establish methods to get rid of this species is a must. The effect of different natural rock minerals; pyrite, magnetite, pyrrhotite, and wurtzite as constituent parts of the Earth’s crust can play a major role in waste treatment. The properties of those minerals towards the behavior of chromium (sorption) were studied under the effect of changes of pH and contact time to treat the waste solution of toxic chromate. The total chromium species in the reaction system was determined using Cr51 as a simpler, faster and more accurate analytical tools. Concerning the effect of types of minerals, the synthetic ones, the results indicated that pyrrhotite and wurtzite were highly effective for the removal of chromate with almost 100 % sorption capacity as it was pH-independent, despite the presence of a degree of reductive ability of both minerals. While, it was 99 % at pH 8.5 and 28 % at pH 3 for pyrite and magnetite, respectively, which was pH dependent. The equilibrium adsorption capacities for chromium adsorption were 0.34 ± 0.15, 0.028 ± 0.01 and 4.27 ± 1.3 mg/g mineral for natural minerals pyrite, magnetite and synthetic one pyrhotite, respectively. However, it was found 117.7 ± 10.9 mg/g for synthetic mineral wurtzite. These results can be attributed to the redox power of oxide and sulfide minerals; magnetite and, pyrite used. For kinetic studies of chromium (VI) adsorption, non linear model approved that the reaction could be described based on pseudo-second-order kinetics in such simulated environmental heterogeneous systems.