. Conclusions
The studied soil was coarse-grained and the total Hg concentration
decreased with increasing particle sizes. However, even the
least contaminated fraction (2–4 mm) substantially exceeded the
Swedish generic guideline value for Hg in soils with less sensitive
use (2.5 mg kg1
). Particle size separation and the use of water
were insufficient to remove Hg to the acceptable levels. As little
as 0.03–0.2% of the total Hg was removed from soil fractions with
water, showing a strong affinity of Hg for soil constituents. No correlation
between the total and dissolved Hg and SOM (both total
and dissolved) was identified for the studied soil.
Although different pH values affected Hg dissolution and an enhanced
Hg desorption was observed at pH 5 and 11, soil washing
by pH adjustment was insufficient for Hg removal, as the highest
amount of mobilized Hg at these two pH values was only up to
0.3% of the total soil Hg. The pH 3 should be avoided for Hg washing
since Hg was shown to be least soluble at this pH. Increased
chloride concentration through addition of 0.1 M HCl acid did not
improve Hg mobilization either in the studied soil.
The best result was obtained by the use of NaOH solution at pH
13, where 1.5% of the total Hg was removed from soil. This, however,
was still not sufficient to reach the acceptable Hg levels in
soil. Mercury was firmly bound to soil particles and the studied soil
washing conditions were not sufficient to extract Hg. Stabilization
techniques should be considered for the future soil treatment.
. ConclusionsThe studied soil was coarse-grained and the total Hg concentrationdecreased with increasing particle sizes. However, even theleast contaminated fraction (2–4 mm) substantially exceeded theSwedish generic guideline value for Hg in soils with less sensitiveuse (2.5 mg kg1). Particle size separation and the use of waterwere insufficient to remove Hg to the acceptable levels. As littleas 0.03–0.2% of the total Hg was removed from soil fractions withwater, showing a strong affinity of Hg for soil constituents. No correlationbetween the total and dissolved Hg and SOM (both totaland dissolved) was identified for the studied soil.Although different pH values affected Hg dissolution and an enhancedHg desorption was observed at pH 5 and 11, soil washingby pH adjustment was insufficient for Hg removal, as the highestamount of mobilized Hg at these two pH values was only up to0.3% of the total soil Hg. The pH 3 should be avoided for Hg washingsince Hg was shown to be least soluble at this pH. Increasedchloride concentration through addition of 0.1 M HCl acid did notimprove Hg mobilization either in the studied soil.The best result was obtained by the use of NaOH solution at pH13, where 1.5% of the total Hg was removed from soil. This, however,was still not sufficient to reach the acceptable Hg levels insoil. Mercury was firmly bound to soil particles and the studied soilwashing conditions were not sufficient to extract Hg. Stabilizationtechniques should be considered for the future soil treatment.
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