Application of Brown Coal and Activated Carbon for the Immobilization of Metal Forms in Soil, along with Their Verification Using Generalized Linear Models (GLMs)

Abstract

Various factors can lead to the transformation of metal forms and to an increase in their solubility and, consequently, their mobility. One solution to the problem of increased solubility is the use of carbons as additives to soil in order to limit the potential migration of contaminants. The aim of this study was to determine the effect of using brown coal and activated carbon on metal forms that are available to plants. The mineral composition of the coals used in a pot experiment was analyzed. Observations were carried out with a JJSM-6380 LA scanning electron microscope (SEM) connected to an EDS electron micro-probe. The total contents of Zn, Cd, Pb and Cu in the assessed soils as well as the content of available metal forms were determined after single extractions with different reagents, namely 1 M NH4NO3, DTPA and 1 M HCl. Generalized linear models (GLMs) were used to evaluate the effectiveness of the stabilization methods in a long-term pot experiment. The carbons reduced the percentage of these forms relative to the total metal content in the soil. After adding brown coal, Zn, Cd, Pb and Cu forms were reduced by up to 32%, 30%, 33% and 43%, respectively. After adding activated carbon, the metal forms of Zn, Cd, Pb and Cu were reduced by up to 47%, 44%, 40% and 50%, respectively. The following order of extracted metal forms with different solutions was found: HCl: Zn > Pb > Cu > Cd; DTPA: Pb > Zn > Cu > Cd; NH4NO3: Zn > Cu > Pb > Cd. Eight years after setting up the pot experiment, the contents of humic substances in soils with the addition of both tested carbons were compared, and the soils with added carbons were found to have a stable content of humic fractions. The costs of remediation through the stabilization method using the tested brown coal and activated carbons do not exceed USD 75/t (taking into account the double doses of both carbons).

Influence of Carbons on Metal Stabilization and the Reduction in Soil Phytotoxicity with the Assessment of Health Risks

“…The dry matter content was 65.69% for brown coal and 94.04% for activated carbon. Carbons are characterized by different contents of metals, which have been confirmed by numerous authors conducting research on brown coal and activated carbon [7,13,32,49]. These researchers [7,13,49,50] have observed the stabilization of soil pH in studies with brown coal on alkaline soils.…”

“…Carbons are characterized by different contents of metals, which have been confirmed by numerous authors conducting research on brown coal and activated carbon [7,13,32,49]. These researchers [7,13,49,50] have observed the stabilization of soil pH in studies with brown coal on alkaline soils. Maintaining high pH values is important to reduce metal mobility and phytotoxicity.…”

“…These observations were confirmed by Brümmer and Herms [55], whose study showed that when the pH value increased, the solubility of the metals decreased in the following order: Cd > Zn > Cu > Pb. In a study conducted with brown coal on alkaline soils, the stabilization of the soil pH, a reduction in the content of the phytoassimilable forms of metals, and a decrease in their percentage share in relation to the total contents of metals in the soil were found [7,13]. For the SC soil, the post-EDTA extraction metal contents were determined as follows: Cu-3.11, Pb-5.63, Zn-< 0.05, Cd-<0.005, Cr-<0.03, and Ni-<0.05 mg•kg −1 d.m.…”

“…Soil is the direct pathway for the contamination of plants by metals [5]. Metals are converted into different forms [6][7][8]. It is assumed that in the soil's solid fraction, only some of the pollutants can negatively influence organisms.…”

Immobilization of Pb by organic and inorganic phosphate and calcium sources in an acidic Pb-polluted soil amended with cow manure

“…Reducing the availability of heavy metals can be an important step in reducing the uptake of heavy metals by the plant. A number of natural and synthetic materials such as carbonates, clay minerals, organic matter, and phosphate compounds have been introduced to evaluate their ability to stabilize toxic metals (10)(11)(12).…”