Molten salt mediated low-temperature direct roasting of spent lead paste

Abstract

Traditional pyrometallurgy for recovery of spent lead paste suffered from high energy consumption, massive reducing agent and toxic SOx gas emission. Here, a sustainable molten nitrate salt mediated approach was proposed to realize low-temperature (500 °C) direct roasting of waste lead paste. Efficient desulfurization could not be realized via single direct smelting of the mixture containing spent lead paste, Na2CO3 and NaNO3. The introduction of Na2CO3 desulfurizer could promote the chemical conversion with PbSO4, while the process still required relatively high temperature above 900 °C to realize relatively high desulfurization efficiency. After the introduction of NaNO3 molten salt into spent lead paste-Na2CO3 system, the original solid-solid reaction in spent lead paste-Na2CO3 system was changed to solid-liquid-solid contract, providing more reaction probability between Na2CO3 and PbSO4 phase in spent lead paste. As a result, high-purity lead oxide powders were obtained with 98.7% desulfurization and 99.2% lead recovery ratio. A profit of $378.2 per ton spent lead paste could be achieved from the economically evaluations. The proposed novel pyrometallurgy approach eliminated the emission of harmful SOx from the decomposition of PbSO4 phase and releases of lead containing wastewater, offering a robust lead oxide recovery substitute from secondary lead resources while possessing significant environmental and economic benefits.