Effect of attapulgite calcination on heavy metal adsorption from acid mine drainage

Abstract

Attapulgite calcined at 973.15K was characterized and utilized as an adsorbent for the removal of heavy metals and neutralization of acid mine drainage (AMD) from a gold mine. Batch adsorption experiments were carried out using a thermostatic shaker. Activated attapulgite showed that it can neutralize AMD as it raised the pH from 2.6 to 7.3 after a residence time of 2 h. Metal ion removal after 2 h was 100% for Cu (II), 99.46% for Fe (II), 96.20% for Co (II), 86.92% for Ni (II) and 71.52% for Mn (II) using a 2.5% w/v activated attapulgite loading. The adsorption best fit the Langmuir isotherm; however, Cu (II), Co (II), and Fe (II) data fit the Freundlich isotherm as well. Calcination at 973.15 K resulted in the reduction of the equilibrium residence time from 4 to 2 h, solid loading reduction from 10 to 2.5% m/v and an increase in maximum adsorption capacity compared with unactivated attapulgite.

Effects of Bentonite Activation Methods on Chitosan Loading Capacity

“…The calcination process causes sequential loss of surface and then bonded water from bentonite, thus releasing more loading sites [10]. From Figure 8, the calcination activation of bentonite can enhance the loading capacity of chitosan.…”

“…The loading of chitosan on bentonite was examined using various reaction times (10-90 min), initial chitosan concentrations (250-2500 mg/L), stirring speeds (50-300 rpm), temperatures (30-50 °C), and pH values (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Specifically, 1 g of raw bentonite clay was dispersed in 150 mL of distilled water.…”

“…The clay was then dried, grinded, and sieved (200 meshes, 0.075 mm sieve size) [15]. To activate the clay by calcination, 5 g of bentonite clay was placed by a griddle in a muffler furnace, and calcinated at given temperature between 150-750 °C for 2 h. After the oven cooled, the clay was grinded and sieved (200 meshes, 0.075 mm sieve size) [10]. For microwave activation, a griddle was used to place 5 g of bentonite clay in a microwave oven.…”

“…The white chitosan particles adsorbed onto the surface of chitosan-loaded bentonite (Figures 11(E) and 11(F)) and into the spaces between the clumps of clay cause the surface to become relatively coarser and looser, and the interlayer distances become significantly larger. These morphological changes indicate that: (1) all three activation methods improve the spatial structure of bentonite; (2) chitosan is loaded via surface adsorption and intercalation; and (3) the loading process does not change the basic structure of bentonite [9][10][11][12].…”

“…low density, the tendency to float, and difficulty in making contact with pollutants [7,8]. On the other hand, various modification techniques, including acid and thermal (by calcination or microwave radiation) treatments, have been reported to affect the adsorption properties of nature clays for metal ions in aqueous solutions [9][10][11].…”