**1. Introduction**

Increasing industrial activities and the lack of appropriate measures to counteract its effects are causing a progressive pollution of air, water and soil with heavy metal emissions. Studies have shown that after the downturn of the industrial activity of metallurgical plant, as is in case of the industrial platform of Targoviste (Romania), heavy metals do not persist in air or water, but tend to concentrate especially in soil and sediment. The heavy metal concentration exceeding the threshold in soil can be considered as risk for human health and remediation technics should be applied to decrease the metal content in soil. The classical methods of soil remediation are expensive and some of them involve the removal of huge volume of soil. An alternative of such methods are the bioremediation methods which involve only eco-friendly materials and procedures, lead to metal recovery with minimal impact on the environment and are cost-effective.

Phytoremediation is a process which uses green plants to remediate the soil polluted with heavy metals or other contaminants. The use of different species of plants in the bioremediation process of polluted soils is an adequate option, with minimal influence over the environment, without destroying the soil, which also provides the opportunity to recover the heavy metals. Phytoremediation is a cheaper method, by 50-80% compared to other methods of bioreme‐ diation [1]. The disadvantage of this method is that it can be a much more slowly process of remediation, requiring several seasons of plant growth. The contaminants may reduce the growth of plants and the resulted biomass, enriched with heavy metals, is potentially harmful in the food chain.

Through the application of phytoremediation on heavy metals polluted soils, the resulting plant biomass will have a high content of toxic metals [2]. This biomass is considered waste and requires controlled and responsible disposal because of the risk of toxicity for environ‐

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ment, and transfer into the food chain. With the decomposition of plant biomass, metals can be washed by rain and transported back into the soil. In order that the phytoremediation process to result in effective outcomes and the level of heavy metals from the environ‐ ment to decrease, not only to move those metals from one area to another, the remedia‐ tion of polluted soils should end with quantitative recovery of metals [3]. The recovery of heavy metals has the advantage of increasing the economic value of the phytoremediation process by transforming this method in a financial self-supporting approach of environmen‐ tal remediation.

There have been numerous studies on the phytoremediation process, having examined the species of plants that have greatest ability to accumulate heavy metals, factors affecting results of phytoremediation and the areas to be covered with plants for remediation purpose, but studies on treatment, storage or use of resulting biomass are insufficient. Some studies presented the possibilities of heavy metal recovery from different waste, even from agricul‐ tural waste. The present research aims to put in one sentence the phytoremediation process and the recovery of heavy metals from the phytoremediation by-products.

The research focused on identifying methods of heavy metal recovery from ash, resulted from the incineration of biomass. The phytoremediation process needs to end up with the heavy metal recovery to obtain (a) de-polluted soil, (b) ash with low content of heavy metals, that can be used as fertilizer in agriculture and (c) amounts of heavy metals that can be recovered in the industry to obtain an economic advantage by financially self-supporting of the phytor‐ emediation process. Because of the lack of researches in this domain, this research was conducted based on the results of those studies that aim to recover metals from different kind of waste (from agriculture, sewage sludge, or woods).
