Recovery of heavy metals from MSW molten fly ash by carrier-in-pulp method: Fe powder as carrier

Abstract

Municipal solid waste (MSW) molten fly ash is classified as a hazardous waste because it contains considerable amount of heavy metals, which pose environmental concern due to their leaching potential in landfill environments. This study proposes Carrier-in-Pulp (CIP) method as a new hydrometallurgical route to extract and recover Pb, Zn, Cu, and Cd from molten fly ash before landfilling. In this method, a carrier material, which recovers the extracted metals, is added simultaneously with fly ash to a leaching solution and is harvested from the pulp by physical separation method, such as magnetic separation or sieving.To demonstrate the effect of the CIP method, shaking flask experiments were conducted under various conditions using NaCl solution, iron powder as carrier, and molten fly ash. More than 99 wt% Pb, Zn, and Cd, and 97 wt% Cu were extracted from the ash.

Recovery of heavy metals from MSW molten fly ash by CIP method

“…Cd from MFA by CIP method (Alorro et al, 2008). These observations agreed with the findings of Reese, K.L.…”

“…The solutions with different concentrations were prepared by dissolving different amounts of reagent grade NaCl powder (Wako Chemical Ltd., Japan) in distilled water. The choice of NaCl as the leaching solution, apart from being a mild reagent, was due to its high affinity to Pb; chloride ion serves as a ligand to extract Pb from MFA (Alorro et al, 2008). The effectiveness of NaCl as a lixiviant for extracting heavy metals from fly ash was reported by Hirosyoshi et al (2004).…”

“…The increase in the metal recovery can be attributed to the larger surface area available for adsorption, which was offered by the higher amount of activated carbon added. It is worthy to note that in the CIP method using Fe powder as carrier (Alorro et al, 2008), negligible amounts of Zn were recovered. Figure 5 shows the amount of metals remaining in the solution phase at different activated carbon dosages.…”

“…On the other hand, unlike the traditional Carbon-in-Pulp process, the carrier or adsorbent in the Carrier-in-Pulp method is not only limited to carbon; other materials such as Fe powder can also be used (Alorro et al, 2008). Furthermore, other physical separation techniques such as magnetic separation can also be employed to harvest the carrier from the leach pulp.…”

“…In an earlier work (Alorro et al, 2008), CIP method using iron powder as the carrier material was applied to recover Pb, Zn, Cu and Cd from molten fly ash. More than 97 wt% of Pb, Zn, Cu, and Cd were extracted from MFA to the solution phase.…”