Book with abstracts from the COST Action 0905 meeting in ... - UMB

THE IMMOBILISATION AND RETENTION OF SOLUBLE ARSENIC,
CADMIUM AND ZINC BY BIOCHAR.
L.Beesley 1 and M. Marmiroli. 2
1 The James Hutton Institute, Craigiebuckler, Aberdeen. AB15 8QH, UK.
2
Department of Environmental Sciences, Section of Genetics and Biotechnologies, University
of Parma, 43100 Parma, Italy.
Keywords: biochar, cadmium, zinc, arsenic, heavy metals, sorption
Water-soluble inorganic pollutants may constitute an environmental toxicity problem if their
movement through soils and potential transfer to plants or groundwater is not arrested. The
capability of biochar to immobilise and retain arsenic (As), cadmium (Cd) and zinc (Zn) from
a multi-element contaminated sediment-derived soil was explored by a column leaching
experiment and scanning electron microanalysis (SEM/EDX). Sorption of Cd and Zn to
biochar’s surfaces assisted a 300 and 45 fold reduction in their leachate concentrations,
respectively. Retention of both metals was not affected by considerable leaching of watersoluble
carbon from biochar, and could not be reversed following subsequent leaching of the
sorbant biochar with water at pH 5.5. Weakly water-soluble As was also retained on biochar’s
surface but leachate concentrations did not duly decline. It is concluded that biochar can
rapidly reduce the mobility of selected contaminants in this polluted soil system, with
especially encouraging results for Cd.
Introduction
Biochar is a low-density charred material
produced by burning biomass under
conditions of low temperatures and minimal
oxygen. Experimental application of this
material to soils to sequester carbon has been
encouraged by its very high organic carbon
content (Yin Chan et al., 2009). There are
wider agro-environmental benefits of adding
biochar to soils, for example, increasing soil
pH and reducing leaching of soluble
macronutrients (Novak et al., 2009).
Application of biochar to real world
contaminated soil systems has received little
systematic investigation to date but initial
trials are encouraging regarding the retention
of both inorganic and organic pollutants
(Beesley et al., 2010). The present study
evaluates the efficacy and permanence of
As, Cd and Zn by biochar in a column
leaching test and by microanalysis
(SEM/EDX).
Materials and Methods
Triplicate bulk soil samples were
sourced from a canal embankment in
Kidsgrove, Staffordshire, UK, with a known
history of heavy metals and As
contamination (Beesley et al., 2010). Six
glass leaching columns (XK50, Pharmacia
Biotech, UK), 20 cm in length and 5 cm in
internal diameter, were packed with 400g of
air-dried soil (two columns) whilst the
remaining four columns were packed to ¾ of
their length with biochar (biochar had far
lower density than soil).
A. B.
------- 300 µm ------- ------- 100 µm -------