lead(II) ion; coal; activated carbon; sorption mechanism; thermodynamics

A sample of activated carbon and two natural coals were studied with respect to the sorption of lead(II) ions from aqueous solutions. Each sample was found to be governed by another immobilisation mechanism for lead(II) ions. For activated carbon AC, interactions of Pb(II) with C? electrons of graphene layers were mainly supposed to manifest a strong exothermic effect (-40 kJ mol-1) and a relatively low degree of reversibility (ca 30 %). Both natural coals were practically of the same acidity, ca 3 mmol g-1. However, only the subbituminous coal (sample H) proved the ion exchange/complexation mechanism as a principal type of lead(II) immobilisation. For such adsorption, full reversibility was experimentally confirmed with adsorption heat of -7 kJ mol-1. The adsorption capacity of sample H was found to be the lowest, representing only 0.08 mmol g-1. Contrary to this, oxidative altered bituminous coal (A) confirmed it had the highest sorption ability to lead(II) ions (ca 0.7 mmol g-1). Its immobilisation mechanism for lead(II) was found to arise mainly from action of a mineral matter in the coal. For such type of sorption, reversibility was found to be about 70 %, with only a slight exothermic heat effect (ca -2 kJ mol-1).

A sample of activated carbon and two natural coals were studied with respect to the sorption of lead(II) ions from aqueous solutions. Each sample was found to be governed by another immobilisation mechanism for lead(II) ions. For activated carbon AC, interactions of Pb(II) with C? electrons of graphene layers were mainly supposed to manifest a strong exothermic effect (-40 kJ mol-1) and a relatively low degree of reversibility (ca 30 %). Both natural coals were practically of the same acidity, ca 3 mmol g-1. However, only the subbituminous coal (sample H) proved the ion exchange/complexation mechanism as a principal type of lead(II) immobilisation. For such adsorption, full reversibility was experimentally confirmed with adsorption heat of -7 kJ mol-1. The adsorption capacity of sample H was found to be the lowest, representing only 0.08 mmol g-1. Contrary to this, oxidative altered bituminous coal (A) confirmed it had the highest sorption ability to lead(II) ions (ca 0.7 mmol g-1). Its immobilisation mechanism for lead(II) was found to arise mainly from action of a mineral matter in the coal. For such type of sorption, reversibility was found to be about 70 %, with only a slight exothermic heat effect (ca -2 kJ mol-1).