Enrichment implication of froth flotation kinetics in the separation and recovery of metal values from printed circuit boards

Abstract

The e-waste printed circuit boards (PCBs) are rich in metal content and processing these wastes for extracting the metal values and removing the non-metallic constituents is a prospective proposition. Froth flotation methodology was observed to be a promising technique for rejecting plastics from the comminution product. It has been shown that nearly reagent-free flotation of relatively coarse size (−1.0 mm) pulverized e-waste is feasible with a reasonably good product at a high yield and excellent recovery. In the present research work, enrichment of ground 1.0 mm PCB powder was investigated through flotation route by varying the operating variables such as frother dosage, pulp density, air flow rate and rotational speed of impeller. The liberation studies accomplish that liberation of metal value from non-metallic constituents at −1.0 mm size is excellent and the particulate system is significantly rich in metal value, containing around 23% metal. In-depth study of froth flotation kinetics is primarily focused on high rejection of plastics and also identification of optimum operating conditions for the same. Single-stage flotation enhances metal content from 23% to over 37%, contributing a mass yield of around 75% with recovery of nearly 95% metal values, suffering nominal loss of around 4% metal value only, while effectively rejecting 32% of the materials in feed through float fraction. The interdependence of kinetics and process variables has been discussed and it has been concluded that a high rotor speed aids efficient rejection of the plastics. However, addition of frother is essential to help stabilize the froth and enhance the kinetics, while efficient pre-concentration is facilitated through a combination of moderate air flow with low pulp density. Generation of pre-concentration through flotation route from the entire −1.0 mm comminution product stands accomplished.