Improving efficiency and feasibility of subcritical water debromination of printed circuit boards E-waste via potassium carbonate adding

[摘要] Waste printed circuit boards (WCBs) were debrominated under hydrothermal treatment, using potassium carbonate as an alkaline additive to improve debromination efficiency (DE). Two different high-pressure reactors were used: a 1-L stirred reactor, where the evolution of the DE was followed over time at a low CO32-/Br- ratio (1:25), and an elementary 0.1-L non-stirred reactor, used to find the optimal parameters and to simplify the hydrothermal debromination (HTD) process. Considering both reactors, experiments were conducted changing the temperature (200 degrees C, 225 degrees C, 250 degrees C, 275 degrees C), and also the CO32-/Br- anionic ratio (1:50, 1:25, 1:10, 1:5, 1:2.5, 1:1, 2:1, 4:1) and the solid/liquid ratio (1:10, 1:5, 1:2) in the case of the 0.1-L reactor. No metallic catalyst was required. A maximum DE of about 98.9 wt % was reached in the agitated vessel at 275 degrees C after 4 h, with an additive/ bromine ratio of 1:25. Similar DE (99.6 wt %) was also achieved in the non-stirred reactor at only 225 degrees C and after 2 h, using an additive/bromine ratio of 4:1 and a solid/liquid ratio of only 1:2. Concerning the solid phase behaviour during debromination, only 5 % of the net calorific value (NCV) was lost after a complete HTD treatment of WCB.

[发布日期] 2021-10-15

[关键词] Hydrothermal process;Debromination efficiency;Printed circuit boards;E-Waste;Alkaline additive;Potassium carbonate