Pyrolysis as a technique for separating heavy metals from hyperaccumulators. Part 1: Preparation of synthetic hyperaccumulator biomass

Phytoremediation involves removing metals from soil or water for environmental reasons and phytomining implies extraction of metals from soils rich in metal content, using hyperaccumulators for economic gain. "Synthetic hyperaccumulator biomass" (SHB) was prepared to mimic the metal concentration and/or chemistry found in actual hyperaccumulators. The purpose for developing a technique to produce SHB was to prepare sufficient quantities of samples for use in lab-scale and pilot-scale pyrolysis experiments. Bench scale experiments were conducted at 27degreesC to incorporate metals like Ni, Zn, Cu, Co, and Cr into 3 g of SHB (milled corn stover) using metal acetate and metal citrate salt solutions. Two parameters, namely concentration of metal salt and soaking time were studied. Suitable acetate and/or citrate feed concentrations and soaking times were then selected for preparing the SHB, containing a particular heavy metal, for lab-scale and pilot-scale pyrolysis experiments. For the lab-scale pyrolysis experiments, 160 g of the SHB was prepared using the five heavy metal acetate and citrate feeds. About 500 g of the SHB was prepared for the pilot-scale experiments using the Ni, Zn, and Cu acetate feeds. Except for lab-scale/Cu acetate feed (6% higher), lab-scale/Cr acetate feed (20% higher), lab-scale/Ni citrate feed (8% lower), and pilot-scate/Cu acetate feed which was 2.2 times higher than the literature value, concentration of metal in the other nine types of SHB prepared for the lab-scale and pilot-scale, pyrolysis experiments was within the hyperaccumulator metal concentration ranges found in the literature. The final goal of this work, which is presented in a series of four parts, is to demonstrate the use of pyrolysis as a first step towards the recovery of heavy metals from hyperaccumulators used for phytoremediation or phytomining. (C) 2003 Elsevier Science Ltd. All rights reserved.