Efficient extraction of metals from thermally treated waste printed circuit boards using solid state chlorination: Statistical modeling and optimization

摘要

Formal recycling of e-waste is necessary for recovery of valuable metals and to avoid environmental damage due to use of toxic chemicals and illegal disposal of the leftovers. This study focused on development of an effective and environment-friendly method to extract valuable metals from waste printed circuit boards (WPCBs) using low temperature solid state chlorination followed by water leaching method. The shredded WPCBs were thermally pre-treated at 600 degrees C to convert plastic fraction into oil and combustible gases. The acquired metal rich residue (T-WPCBs) was chlorinated subsequently with NH4Cl. A combination of central composite designresponse surface methodology (CCD-RSM) was successfully implemented into modeling the chlorination process for extraction of Au and Cu as a function of the process variables viz. temperature, time and NH4Cl dose. More than 96% of Cu and 67% of Au were extracted with water, when the T-WPCBs powder was chlorinated with 3 g/g of NH4Cl at 300 degrees C for 3 h. However, the proposed process has potential to extract other metals also; hence, the added credibility of the process was revealed by reporting extraction of other valuable metals such as Ni, Fe, Pb, Ag, and Zn at optimized conditions. This study strives to develop a closed loop process for extraction of metals; therefore, NH4Cl, the lone chemical used herein, was recycled for an economically viable process. Unlike the traditional pyrometallurgical process, which operates above 1000 degrees C and produces toxic fumes and soot, this process works at a low temperature range of 275-325 degrees C and able to extract out more than 90% of the total metal content without generating any toxic fume and soot.