**5. Material and method**

The present study was conducted on seven perennial grass species from *Juncaceae* and *Poaceae* family, to find the best solutions for the phytoremediation of soils in the vicinity of metallur‐ gical plant of Targoviste (Figure 3). The aim of research was to evaluate the capacity of these plants species to accumulate heavy metals which were found in high concentrations (above the normal range in agricultural soils) on the studied site. The best accumulative species, *Lolium perenne* was used in an experiment of heavy metal extraction from plant biomass to test the efficiency of metal recovery methods in case of phytoremediation procedure.

**Figure 3.** Studied area in the vicinity of metallurgical plant of Targoviste

#### **5.1. Research course**

Sampling points of plants and soil were chosen so that the results to reflect a snapshot of the impact of metallurgical activities in this area by particles emissions. Sampling was done at distances between 500 and 1000 meters from the source of pollution, from three different points, chosen according to triangle method. The results of metal concentration represent the average of these three samples. The depth of sampling was chosen according with the depth to which the roots of plant culture normally develop. Was formed a mean sample from the column of soil between 0 – 20 cm depth.

Plants were harvested in two seasons, summer and autumn 2008. Was harvested the entire plant, including the root system. For each plant sample, the soil underneath was collected, down to the horizon where the plant developed its root system. The soil was used to establish the bioaccumulation factor of each plant species by comparing the metal concentration in plants with the metal concentration in soil.

The harvested plants were wild growing species which already were adapted to high pollution level of the soil. They were perennial grasses, which usually are used as forage for animals: *Lolium perenne, Festuca pratensis, Stipa capillata, Agrostis alba, Cynodon dactylon, Agrostis tenuis* and *Luzula campestris*.

The plants and soil samples were processed in the laboratory for elemental analysis by ICP-AES (see section 5.2). After harvesting, the fresh plants sample were cleaned with deionized water to remove the soil particles, dried at 60 °C for few hours, ground to a fine powder and analyzed to establish the metal concentrations. The soil samples were dried at 40 °C for 24 hours, ground to a fine powder, sieved at 250 µm (according to SR ISO 11464).

Based on the results of bioaccumulation for studied plant species, *Lolium perenne* was chosen for the subsequent experiment for heavy metal recovery. In the vicinity of metallurgical plant, a 10x10 m experimental plot was cultured with this species. During the growing period no amendments were added. After one growing season, the plants were mowed and used for the experiment of heavy metal extraction by hydrometallurgical and electrochemical processes.

**Figure 4.** Plant biomass incineration: (a) heat treatment oven with forced rod, (b) incineration process

First the plants were dried for few hours, at 105 °C to remove the water and to decrease the biomass volume [45]. After drying stage, the plants were incinerated in alumina crucibles using a heat treatment oven with forced rod (Figure 4), nominal voltage of 220 V, nominal amperage of 30 A, and maximum temperature 1300 °C. The incineration was conducted at temperature between 400 °C and 600 °C in two stages. The first stage was the heating up to 500 °C for 30 minutes, followed by a 90 minutes of burning at temperature of 500 - 600 °C. Weighing was made for the raw biomass, for the biomass after drying and after incineration to establish the percentage of dry matter and percentage of ash.

**Figure 5.** Electrolyses cell

gical plant of Targoviste (Figure 3). The aim of research was to evaluate the capacity of these plants species to accumulate heavy metals which were found in high concentrations (above the normal range in agricultural soils) on the studied site. The best accumulative species, *Lolium perenne* was used in an experiment of heavy metal extraction from plant biomass to test the

Sampling points of plants and soil were chosen so that the results to reflect a snapshot of the impact of metallurgical activities in this area by particles emissions. Sampling was done at distances between 500 and 1000 meters from the source of pollution, from three different points, chosen according to triangle method. The results of metal concentration represent the average of these three samples. The depth of sampling was chosen according with the depth to which the roots of plant culture normally develop. Was formed a mean sample from the

Plants were harvested in two seasons, summer and autumn 2008. Was harvested the entire plant, including the root system. For each plant sample, the soil underneath was collected, down to the horizon where the plant developed its root system. The soil was used to establish the bioaccumulation factor of each plant species by comparing the metal concentration in

The harvested plants were wild growing species which already were adapted to high pollution level of the soil. They were perennial grasses, which usually are used as forage for animals: *Lolium perenne, Festuca pratensis, Stipa capillata, Agrostis alba, Cynodon dactylon, Agrostis tenuis*

The plants and soil samples were processed in the laboratory for elemental analysis by ICP-AES (see section 5.2). After harvesting, the fresh plants sample were cleaned with deionized water to remove the soil particles, dried at 60 °C for few hours, ground to a fine powder and

efficiency of metal recovery methods in case of phytoremediation procedure.

**Figure 3.** Studied area in the vicinity of metallurgical plant of Targoviste

column of soil between 0 – 20 cm depth.

318 Environmental Risk Assessment of Soil Contamination

plants with the metal concentration in soil.

**5.1. Research course**

and *Luzula campestris*.

Leaching of ash was made by mixing 10 g of ash with 200 ml of nitric acid (HNO3), concentrated to 65%. The mixture was heated to boiling point for 60 minutes and then cooled down to room temperature. After complete cooling, in the mixture were added, on ice, 200 ml of concentrated sulfuric acid (H2SO4). After half an hour of rest, the mixture was filtered.

For the extraction of heavy metals, an electrolytic cell was designed (Figure 5), with stainless steel electrodes and 200 ml of the filtrate obtained from the leaching of the ash as electrolyte. The electrolysis was carried out for 90 minutes with an electric intensity of 1.5 A, and a voltage of 11.4 V. The microscopic and gravimetric methods were used to assess the metal deposition on electrodes.
