Recycling lead from waste lead-acid batteries by the combination of low temperature alkaline and bath smelting

Recycling lead from waste lead-acid batteries has substantial significance in environmental protection and economic growth. Bearing the merits of easy operation and large capacity, pyrometallurgy methods are mostly used for the regeneration of waste lead-acid battery (LABs). However, these processes are generally operated at the temperature higher than 1300 degrees C. To shorten the energy consumption, a novel pyrometallurgy process which consisted of low temperature alkaline and bath smelting was proposed in this work. The reduction of lead and smelting of slag system are the key factors determine the energy consumption. Thermodynamic calculation suggested that the addition of Na2CO3 can make the reduction of PbSO4 spontaneously at the temperature higher than 288 degrees C (PbSO4 -> PbCO3 -> PbO -> Pb), while direct reduction of PbSO4 necessitated the temperature higher than 1499 degrees C (PbSO4 -> PbO -> Pb). To achieve the efficient reduction of PbSO4, the molar ratios of C/PbSO4 and Na2CO3/PbSO4 should be higher than 0.5 and 1.0, respectively. Meanwhile, a new smelting system (i.e., FeOSiO2-CaO-Na2O) was established in the presence of Na2CO3. Phases with low melting temperatures, such as NaFe2O3, Na2FeSiO4, Na2Ca2Si2O7, Na14Fe6O16 and Na0.5FeO2, were formed. The melting temperature of Fe-SiCa-Na system was lowered to 1050 degrees C at the mass dosage of Na2CO3 at 30%. Recovery of lead under various reduction conditions were systematically evaluated. Under optimum operational conditions, i.e., the dosages of C and Na2CO3 at 10% and m(actual)/m(theory) ratio of 1.3 (all in mass), smelting temperature of 1050 degrees C, and smelting time of 75 min, respectively, the lead recovery efficiency reached >98.0%. Moreover, this method has been successfully applied for the industrial recovery of lead at the scale of 200, 000 tons annually since 2019. Taken together, this method is robust for recovery of lead from the waste LABs and is helpful for building the resource-conserving society.