Removal of heavy metals and neutralisation of acid mine drainage with un-activated attapulgite

Unactivated attapulgite was characterised and utilised as an adsorbent for the removal of heavy metal and neutralisation of acid mine drainage (AMD) from a gold mine. Adsorption experiments were carried out by agitation of a fixed amount of attapulgite with a fixed volume of AMD in a thermostatic shaker for varying times. Attapulgite showed that it can neutralise acid mine drainage as the pH after 4 h was 7.11. The results showed that metal ion removal after 4 h was 100% for Cu(II) and Fe(II), 93% for Co(II), 95% for Ni(II) and 66% for Mn(II) using a 10% (w/v) attapulgite loading. The experimental data best fit the Langmuir Isotherm with maximum adsorption capacities for Cu(II), Co(II), Mn(II), Fe(II) and Ni(II) being 0.0053, 0.0044, 0.0019, 0.01, and 0.0053 mg/g, respectively. The adsorption process fitted well the pseudo first order kinetics for Co(II) and Cu(II) and pseudo second order for Ni(II), Mn(II) and Fe(II). Thermodynamic data show that Cu(II), Co(II), Fe(II) and Ni(II) adsorption was thermodynamically spontaneous whilst Mn(II) was not thermodynamically spontaneous. The process is endothermic for Cu(II), Co(II), Mn(II), and Ni(II) and exothermic for Fe(II). Spent attapulgite (attapulgite that has already been used to remove metals) could be reused twice without regeneration.