RESUMO
In this contribution, maximum capacity for adsorption of Pb(2+), Ni(2+), and Cu(2+) by silkworm chrysalides (SC) was determined. The raw silkworm chrysalides (SC(r)) and chrysalides after acidic washing (SC(w)) were used. Chitin (CT), extracted from SC, and chitosan (CS), with 85% deacetylation, were employed as reference samples. Adsorption tests showed that all the studied adsorbents exhibited excellent performance in removal of metals. The choice of a more appropriate adsorbent is related to its efficiency for removal of a specific metal. The studied materials presented different intensities for metal adsorption as follows: (i) Ni(2+)>Cu(2+)>Pb(2+) for SC(r); (ii) Pb(2+)>Cu(2+)>Ni(2+) for SC(w); (iii) Ni(2+)>Cu(2+)>Pb(2+) for CT; and (iv) Cu(2+)>Pb(2+)>Ni(2+) for CS. Metal adsorption onto SC(r) and CS was analyzed by Freundlich and Langmuir isotherm equations. Adsorption values for CS-Pb and SC(r)-Ni were provided by the Freundlich model, while the adsorption values for CS-Cu, CS-Ni, SC(r)-Pb, and SC(r)-Cu were provided by the Langmuir model. The studied adsorbents are suitable for use in treatment of wastewater. From the economic point of view, the use of SC(r) as an adsorbent of heavy metals (mainly Ni(2+)) on the large industrial scale would be more appropriate.