关键词: 火试金灰皿, 铅, 乙酸, 浸出, 动力学

Abstract: The fire assay cupel containing heavy metal lead is an intermediate waste product in the process of cupellation. The comprehensive disposal of cupel waste with high lead content is of great significance to reduce heavy metal pollution and recycle lead. The metal oxides mainly exist in the form of Al2O3 and sintered MgO in the fire assay cupel, and the melting points are 2054 and 2852℃, respectively, which seriously affects the normal process of melting. The wet process can effectively avoid the influence of magnesia-aluminum oxides with high melting point substances. Because of resource and harmless treatment of fire assay cupel, the thermodynamic of lead leaching is analyzed, the effects of excess coefficient of acetic acid, leaching temperature, reaction time, stirring speed, and liquid-solid ratio on the leaching rate of lead were investigated and leaching kinetics of lead were studied in the acetic acid-H2O system. With the increase of the mole fraction of acetate ions, lead ions and acetate ions in an aqueous solution are easily complexed to form a lead acetate complex which is difficult to ionize, and the concentration of lead ions in the solution decreases, which promotes the leaching reaction of lead to a certain extent. Under the optimized condition that the excess acetic acid coefficient of 1.6, the liquid-solid ratio of 6:1, the leaching temperature of 80℃, the stirring speed of 200 r/min, and the reaction time of 40 min. By first leaching and secondary leaching to the leaching residue, the primary leaching rate of lead is 98.31%, the secondary leaching rate is 95.53%, and total leaching efficiency reached 99.96%. The leaching process of lead is consistent with the shrinking particle model and controlled by diffusion, conforms to the kinetic equation 1-2/3φ-(1-φ)2/3=kt, the calculation result of apparent activation energy is 38.949 kJ/mol.

Key words: fire assay cupel, lead, acetic acid, leaching, kinetics