**7. Remediation of lanthanide waste and their recovery**

In countries with sufficient sources of lanthanides (mainly China), these elements are used as fertilizers to increase agricultural production. With increasing consumption, waste with varying contents of different lanthanides has increased significantly and rapidly. The most important of these are magnets (neodymium), metal alloys (europium and yttrium), batteries, glass, and catalysts (cerium and lanthanum) [126]. Other important sources of lanthanide waste are phosphate mineral fertilizers, industrial wastewater, sewage sludge, mining processes, or wastes from industrial aluminum production [4, 18, 26–29]. Lanthanides present in ecosystems from agricultural production can thus penetrate into the groundwater and migrate to rivers and lakes [58] or to the sea [127]. Some studies on ecological effects and potential threats due to the bioaccumulation of lanthanides have been described, but they are not long-term enough to draw any general conclusions [128, 129]. Relevant regulations or standards concerning doses and threshold values for the presence of lanthanides in the environment have also not been established [38]. In China, lanthanides are cited as the main source of environmental contamination [130]. They are also considered to be emerging pollutants outside of China, requiring the specification of threshold values for concentrations and emissions of lanthanides in the environment [64, 131]. Removing these lanthanide contaminants is therefore a very important requirement in order to reduce the ever-increasing environmental burden on the aquatic environment.

In addition to this very important requirement for remediation, the need for recycling of lanthanides from any (not only liquid) industrial production waste becomes even more acute. One reason is the risk of reduced availability of resources (China owns more than 95% of natural sources) or their relatively rapid depletion from other sources. Replacement of lanthanides with alternate substances in industrial applications is currently not possible [132, 133]. Due to their unique chemical and physical properties and their extensive applications in industrial products, the importance and demand for these elements is constantly increasing [131, 134]. The economic impact of an emerging lanthanide shortage increases the urgency for efficiently using renewable energy sources from the ever increasing number of different types of waste products worldwide. At present, research is focused on the progressive and costefficient recycling of lanthanides for industrial processes [4, 95, 102, 135, 136], which would reduce risks associated with inaccessibility or depletion of natural resources while minimizing environmental problems associated with their extraction and processing [137].

One of the most widespread lanthanide-containing wastes is electrical and electronic equipment, including lighting equipment, computers, or photovoltaic panels. This waste is a growing threat to the world's environment, and lanthanide recovery is therefore becoming economically attractive. The main sources for recycling are luminophores, powder mixtures obtained from electronic waste and containing high concentrations of lanthanides. Luminophores are obtained from television screens or monitors, as well as energy-saving bulbs and lamps, where they are used to convert cathodic tube radiation or ultraviolet electric discharge into mercury vapor and visible light. These luminophores occur as a powder attached to the inner surfaces of mesh or tubes. The glass parts of these waste networks, monitors, screens, and light bulbs can be easily recycled, but luminophore layers must be removed because the luminescent compounds would reduce the quality of recycled glass. The luminophores as waste represent a toxicity problem but, on the other hand, are a concentrated source of various lanthanides, either in the form of dry powder or wet mud [138].

#### **7.1. Chemical recycling**

New techniques of dephosphatisation of the environment include the use of Ln-modified clays [83, 84]. The advantage of these methods is the low level of side effects on living organisms. The unique chemical features of lanthanides make them ideal tracers for geochemical processes in nature [9]. They represent alternative, nonradioactive, highly detectable labels. They were used, for example, to confirm the impact of cyanobacterial mats on deep waters outside French Polynesia, providing evidence for an end-ascending flow [114]. They enable scientists to follow oceanic cycles, petrogenesis, the chemical evolution of the Earth [16, 29], or palaeo-environmental conditions [115–118]. Lanthanides can also serve as anthropogenic activity indicators [27]. Because of their particular affinity to algae, the lanthanide profile may be a useful indicator for exploring the ecology of marine environments [10] and can also be used to monitor sources of pollution from natural events such as volcanic activity [25]. In combination with macroalgal sampling, the lanthanide profile may help to characterize coastal water quality and pollution [22, 23, 27].

Lanthanides have been used for their inert nature as detection agents in various experiments, for example, in studies of the rate of passage and digestibility of nutrients in humans and animals [119–121]. Lanthanide oxides have been used as markers in sea cucumber (*Apostichopus* 

In the development of new, sensitive detection methods, active chelates of lanthanides have been obtained and tested. They are used in sensitive immunoassays to suppress the background [122] or as very sensitive fluorescence probes [123]. An example of their use is the

In countries with sufficient sources of lanthanides (mainly China), these elements are used as fertilizers to increase agricultural production. With increasing consumption, waste with varying contents of different lanthanides has increased significantly and rapidly. The most important of these are magnets (neodymium), metal alloys (europium and yttrium), batteries, glass, and catalysts (cerium and lanthanum) [126]. Other important sources of lanthanide waste are phosphate mineral fertilizers, industrial wastewater, sewage sludge, mining processes, or wastes from industrial aluminum production [4, 18, 26–29]. Lanthanides present in ecosystems from agricultural production can thus penetrate into the groundwater and migrate to rivers and lakes [58] or to the sea [127]. Some studies on ecological effects and potential threats due to the bioaccumulation of lanthanides have been described, but they are not long-term enough to draw any general conclusions [128, 129]. Relevant regulations or standards concerning doses and threshold values for the presence of lanthanides in the environment have also not been established [38]. In China, lanthanides are cited as the main source of environmental contamination [130]. They are also considered to be emerging pollutants outside of China, requiring the specification of threshold values for concentrations and emissions of lanthanides in the environment [64, 131]. Removing these lanthanide contaminants is therefore a very important requirement in order to

*japonicus*) grown on a variety of macroalgal diets [121].

**7. Remediation of lanthanide waste and their recovery**

reduce the ever-increasing environmental burden on the aquatic environment.

In addition to this very important requirement for remediation, the need for recycling of lanthanides from any (not only liquid) industrial production waste becomes even more acute.

labeling of the cyanotoxin microcystin [124, 125].

96 Lanthanides

Lanthanides from waste sources can be recycled by chemical separation from solutions (e.g., chemical precipitation, electrochemically, membrane division, reverse osmosis, etc.). These methods are comparatively costly and, moreover, are often a source of other nonorganic wastes [139]. Methods such as pyrometry and hydrometallurgy for the extraction of lanthanides from ores have significant negative impacts on the environment and involve high costs [126]. The other serious disadvantage is the dependence on a single and limited source and possibly the depletion of other natural resources [126, 140, 141]. These traditional physicochemical processes are expensive or even inefficient for the treatment of sewage containing low concentrations of metal ions [142]. A by-product of conventional methods is the associated large volume of contaminated water, high temperatures and a high consumption of chemical compounds [143, 144]. Researchers are therefore looking for low-cost approaches and at the same time environmentally friendly technologies.

#### **7.2. Biosorption**

As a biotechnological approach, biosorption is considered to be a more efficient and cheaper alternative to conventional chemical methods of recycling lanthanides [133, 145, 146]. Various different organic residues of animal or plant origin, including resin, activated charcoal, or biomass of various organisms (algae, fungi, and bacteria), have been shown to adsorb different lanthanides and have been tested as biosorbents [95, 98, 132, 147]. The development of effective biological methods for lanthanide regeneration from these materials was proven in the aerobic, genetically modified bacterium, *Caulobacter crescentus* [148]. The use of various other biosorbents, including algae, bacteria, fungi, and yeasts, has also been evaluated [149]. Seaweeds, especially brown seaweeds, have been identified as strong biosorbents due to the presence of binding sites for chemical moieties such as carboxyl, amine, and hydroxyl groups [86]. Marine macroalgae are particularly important [150, 151]. For example, Oliveira et al. and Oliveira and Garcia [97, 152] evaluated the potential of *Sargassum* sp. biomass for biosorption of Eu, Gd, La, Nd, Pr, and Sm. They observed the rapid and efficient recovery of these metals, even though they were unable to separate them. The authors suggested that carboxyl groups present in alginates (the main component of the cellular brown algal wall) are the major reactive functional groups. Similar results were obtained with other brown seaweed such as *Sargassum* spp. [16, 96, 102, 135] and *Turbinaria conoides* [98]. Some unicellular algae such as *Chlorella* spp. and *Nannochloropsis* spp. and cyanobacteria *Microcystis* spp. were also shown to be active biosorbents of lanthanides (La3+ and Ce3+) [19, 153]. The disadvantage of adsorption methods, including biosorption, is the generation of secondary wastes similar to chemical approaches although at a considerably lower rate, the subsequent processing of which is often financially demanding [154].

lanthanides [162]. *G. gracilis* was able to effectively remove low concentrations (0.5 mg/L) of lanthanides with 70% yield. The ability of *G. gracilis* to remove lanthanides (Y, Ce, Nd, Eu, and La) from such low concentrations in waste water therefore has the potential to overcome one of the greatest difficulties in recycling these elements so far [162]. It seems therefore promising to use live algae for lanthanide accumulation as an alternate technology for simple and

Lanthanides and Algae

99

http://dx.doi.org/10.5772/intechopen.80260

Algae are very important organisms in terms of ecology, being at the very beginning of the food chain. Their relationships with metals therefore affects other living organisms. Their ability to accumulate lanthanides may have an impact on the surrounding environment, representing both a threat and an opportunity, with the potential for further study and use. As bioaccumulation abilities and beneficial or toxic effects of lanthanides differ in individual algal strains, it is difficult to predict specific ecological hazards. Algae in combination with lanthanides offer a wide variety of applications. They can be used as bioindicators, fertilizers, toxin detectors, or for phytoremediation and recycling. Therefore, understanding the relationships between algae and lanthanides is very important. Once we understand the molecular

We thank Prof. John Brooker for critical reading and language corrections of the manuscript.

The Czech Academy of Sciences, Institute of Microbiology, Centre Algatech, Laboratory of

[1] Oliveira RC, Guibal E, Garcia O. Biosorption and desorption of lanthanum(III) and neodymium(III) in fixed-bed columns with *Sargassum* sp.: Perspectives for separation of

rare earth metals. Biotechnology Progress. 2012;**28**:715-722

This work was supported by the National Program of Sustainability I, ID: LO1416.

Milada Vítová\*, Mária Čížková and Vilém Zachleder

\*Address all correspondence to: vitova@alga.cz

Cell Cycles of Algae, Třeboň, Czech Republic

mechanisms of their effects, we will have greater opportunities for their use.

efficient recycling from wastewater.

**8. Conclusions**

**Acknowledgements**

**Author details**

**References**

#### **7.3. Accumulation in living cells**

Methods for the recycling of lanthanides via living cells offer an alternative, which does not have the disadvantages of chemical and adsorption approaches. Accumulation of lanthanides from the environment is cost-effective and does not produce any substantial secondary waste. In addition, it is a great advantage that it can also be effective in water containing very low lanthanide concentrations, which is problematic in other approaches.

Waste solutions containing lanthanides often have high acidity. Thus, the discovery that the sulfothermophilic red alga *Galdieria sulphuraria* can effectively accumulate lanthanides from various waste solutions, in which no other organisms can grow, was of great importance [155]. The unicellular red alga *G. sulphuraria* can grow autotrophically or heterotrophically in a wide range of different sugars or polyols at a pH of about 1.5 and a temperature of 56°C [156–158]. The ability to accumulate lanthanides was demonstrated in aqueous solutions containing a mixture of Nd3+, Dy3+, and La3+ at pH 2.5, with an efficiency greater than 90% and at a lanthanide concentration of 0.5 ppm [155]. The efficiency remained unchanged at pH values in the 1.5–2.5 range. The authors also showed that lanthanides accumulated inside the cells not only by adsorption to the cell walls, but also by other mechanisms. Although the alga *G. sulphuraria* is indispensable for the treatment of waste solutions that prohibit the growth of most other living organisms, the species is virtually unusable for remediation of most natural water resources, particularly marine water due to its requirement for growth at a low pH. The marine green alga *Ulva lactuca* has been found to remove toxic metals (Cd, Pb, and Hg), and this approach is cost-effective and more efficient than passive adsorption using nonliving biomass [159–161].

Up to now, only one paper has been published demonstrating the high potential of seaweed (in this case, brown algae *Gracilaria gracilis*) to remediate sea water contaminated with lanthanides [162]. *G. gracilis* was able to effectively remove low concentrations (0.5 mg/L) of lanthanides with 70% yield. The ability of *G. gracilis* to remove lanthanides (Y, Ce, Nd, Eu, and La) from such low concentrations in waste water therefore has the potential to overcome one of the greatest difficulties in recycling these elements so far [162]. It seems therefore promising to use live algae for lanthanide accumulation as an alternate technology for simple and efficient recycling from wastewater.
