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Rare earth elements (REEs) have recently received significant attention due to their irreplaceable industrial application for the number of crucial advanced technologies in production of permanent magnets, batteries, luminescence lamps, lasers and other electronic and electrical goods. These technologies have been strongly affecting present consumption of REEs as well as looking for alternative sources, that would guarantee their sufficient supply for the future demand. This study investigates one of the possible and widely employed techniques for the efficient and at the same time, environmentally friendly recovery of REEs by adsorption using bio-based adsorbents. Overall, three bio-sorbents with different composition (residual biomass originated from agriculture and bio-refineries) were examined to study removal efficiency of the 7 most commonly used REEs in mixed aqueous solution. Batch adsorption experiments were carried out at the room temperature, varying the pH value (pH=1,54; 4,24) and different initial concentration of REEs to determine optimum condition for their recovery. Results revealed that removal efficiency for most of the REEs was much higher at pH=4,24 and reached 70-100% for the minimal concentrations and 30-40 % at maximal initial concentrations respectively. Adsorbent containing residual biomass and chitosan showed to be the most effective bio-sorbent for recovery of most of the REEs. In order to describe and fit the obtained data Langmuir and Freundlich isotherms models were employed.

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In this paper, it is proposed to use the biomass of microalgae Chlorella sorokiniana as a biosorbent for wastewater treatment, as well as an oral sorbent. Biosorbents are capable of adsorbing both organic and inorganic compounds, including heavy metals. The sorption capacity depends on the type of aquatic plant and microalgae strain. The use of microalgae and aquatic plants as biosorbents for pollutant treatments is discussed in the introduction part. The biomass of microalgae Chlorella sorokiniana was chosen as the object of this study. The cultivation conditions (temperature, light, pH and aeration) and the optimal biomass harvesting parameters are presented. Dehydration of biomass was carried out in two ways: IR-drying and freeze-drying. The obtained samples were tested for the ability of the biomass to extract heavy metal ions (zinc, cadmium, zinc, copper) from standard solutions. The initial concentration of heavy metal ions in the working solutions was 10 mg/l. Results show that the lyophilized samples demonstrated up to 99.9% of heavy metal removal efficiency. The paper also presents the composition of Chlorella sorokiniana biomass, in which up to 40.97-41.87% are proteins. The analysis of the amino-acid composition showed a ratio of essential to non-essential amino-acids higher than 0.8. All the above results confirm the possibility of using microalgae biomass as an oral sorbent and as an additive in the production of functional foods.

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