T.C.L.P. Test for Assessing Ionic Strength Effects Upon Sorption of Inorganic Contaminants On Red Mud.

We evaluated the effect of ionic strength (IS) upon the adsorption of Zn, Cu, Cd, Pb, As, and P on red mud (RM), by implementing the toxicity characteristic leaching procedure test (TCLP) followed by a semi-total digestion (STD). Adsorption was performed in low IS (47 mM) and high IS (470 mM), using nitrate salts for cations and sodium as the accompanying cation for anions. Cation and anion desorption was evaluated by adding Ca(NO₃)₂ and NaCl solutions to the remaining adsorption residue, followed by the TCLP test and STD. TCLP test was performed with 98.9 mM acetic acid and 64.3 mM NaOH, pH 4.93±0.05, and SD in a microwave oven using 9 mL of HNO₃ and 3 mL of HCl according to the USEPA3051A method. The quality control was performed using NIST SRM 2710a. Mass balance was performed by summation of TCLP and STD, with further comparison with the semi-total estimated concentration (STE). The TCLP test followed by STD differed from low and high IS only for Cu and the TCLP/STD ratio differed for Zn and Cu. The TCLP extracted approximately 26% of Cd, 11% of Cu, 8% of Pb, 7% of Zn, 1% of P, and 0.1% of As, compared with the STD. The recovery (mass balance) was near 100% for Cu and within 88-112% for the others. The TCLP procedure implemented in RM after sorption and desorption presented Cd, Pb, and As values above the maximum concentration of contaminants considered toxic, exceeding the following regulatory limits (mg L^-1): Cd = 1, Pb = 5, As = 5. Therefore if RM is to be used as an adsorbent of contaminated solutions, its disposal must be done carefully because high concentrations of Cd, Pb, and As may be present in the leachate. Sponsored by CNPq, CAPES and FAPEMIG.