Hidden champions of botany

Phytomining

Natural gold diggers

Phytomining: Natural gold diggers

Metal mining by means of plants
Eco-friendly and low-cost
Research still in its infancy

Plants as miners clawing raw materials from the Earth: Phytomining is the name of this field of research that’s based on the discoveries of British botanist Alan Baker and U.S. research agronomist Rufus Chaney four decades ago. While having been largely uneconomical so far, phytomining using so-called hyperaccumulator plants has literally begun to sprout again lately due to heavy raw material price increases.

Alyssum murale

100 kg nickel from 500 kg ash
Economical at 0.1% and higher concentration in the soil
Profitability of conventional mining starts only at 1% concentration

One of these floral miners is Alyssum murale. The “weed” is grown on fields, harvested and dried, for instance around Lake Ohrid in Albania that’s severely contaminated by heavy metals. By burning the residues of the plants, 500 kilos of the ash can yield 100 kilos of valuable nickel that’s needed for rechargeable batteries and paints for example. Although the yield from deep mining is much greater, biomining is a lot more eco-friendly.

Pycnandra acuminata

25% nickel content in the sap
Grows only in New Caledonia
One of 65 nickel-hyperaccumulating species in New Caledonia

Another nickel digger is Pycnandra acuminata, a tree that grows on New Caledonia’s main island. A fourth of its sap consists of nickel.

Phalaris arundinacea

Very high energy content for biogas
3 mg germanium from 1 kg plant
Specially bred strains are supposed to multiply the current yield

The “harvesting of metals” such as cobalt, tellurium, thallium and rare-earth elements by now includes the systematic breeding of special plant species. One of these experts is Phalaris arundinacea (aka reed canary grass) whose roots go down as far as 3.5 meters into the ground. It specializes in the semimetal germanium, which is required for fiber optic cables, infrared sensors, chips and solar cells. Specially bred strains are supposed to multiply the current yield.

Mustard plant

57 g pure gold from 1,000 kg plant ash
Gold nanoparticles for high-tech industries
So far only in laboratories

For centuries, scientists have been trying to make gold by artificial means or to convert other metals into gold using chemical processes -- without success so far. Now, phytomining comes into play: Plants are supposed to serve as gold diggers. The noble metal can be extracted from the mustard plant, albeit in such tiny amounts that it’s not profitable.

Phytoremediation

Green poison aspirators

Phytoremdiation: Green poison aspirators

Plants extract contaminants from the soil
More than 500 known plant species
Re-cultivation of contaminated industrial soil

Cadmium, lead, zinc, nickel, platinum or palladium – around the world, countless areas are contaminated by toxic metals from industrial and military operations or farming. In Germany alone, there are 300,000 such areas. Soil cleanups cost enormous amounts of money. Maltreated Mother Nature herself, though, provides a remedy: plants that “suck” contaminants from the soil – referred to as phytoremediation in professional jargon. However, this form of decontamination is a slow process that takes years. Therefore, the objective is to breed plants with large leaves that suck larger amounts of contaminants from the soil to make it usable again in less time.

Arabidopsis halleri

Decontamination of agricultural soil
Cadmium, lead, zinc, nickel, copper
Ash contains up to 20% metals

Arabidopsis halleri can absorb high concentrations of heavy metals that would be highly toxic to humans and animals. In this way, it protects itself against herbivores. Arabidopsis halleri thrives on the perimeters of shut-down mines, old steel mills and abandoned industrial areas.

Common water hyacinth

Deposits arsenic in its roots
Purifies drinking water by extracting arsenic
Usable as a living plant or powder

Even aquatic plants may be used for phytoremediation. The common water hyacinth, originally an invasive species introduced from South America, absorbs toxic substances in water and purifies drinking water by extracting arsenic, for example. Research scientists have found that powder from the dried roots of just one common water hyacinth plant is sufficient to filter out arsenic from water.

Sunroot

Grows very fast
Usable against cadmium, lead, nickel, copper and zinc
High energy content: 20 metric tons equate to 6,400 liters of heating oil

The fast-growing edible plant with its potato-like tubers even thrives on barren soil. Its origins are in North and South America. The Jerusalem artichoke absorbs large quantities of various heavy metals in its roots, sprouts and tubers. In addition, the plant is suitable for producing bioethanol.

Filtration

Air cleaners

Filtration: Air cleaners

Air cleaning by means of plants
They filter up to 95 % of harmful substances from the air
such as formaldehyde, benzene, nicotine, trichloroethylene, etc.

That plants make for a pleasant and comfortable atmosphere is a well-known fact. However, they can do a lot more than just look pretty: They store fine dust particles and gases like CO₂ and nitrogen that are harmful to climate and health and transform them into oxygen by means of photosynthesis.

Moss

Binds hydrogen, CO₂, fine dust particulate, etc.
Temperature-independent from –30 to +70 degrees C
Is regarded as a means of storing and controlling water

In our own gardens or yards, it’s typically very unpopular and hard to get rid of. But moss can actively help protect the environment. Since moss has no roots, the plant extracts its nutrients from the air. They include nitrogen, carbon dioxide, fine dust particles and other emission components. In the Sion electric car from Sono, moss is supposed to serve as an air filter for the interior. The idea: Due to the negative charging of the moss, positively charged particulate is filtered out of the air. Microfiber cloths, by the way, work according to a similar principle.

Green lily

Was investigated by NASA as an air filter in space stations
House plant, not hardy
Also eliminates toxic substances like xylolene and toluene in the air

The green lily that has its origins in South Africa filters up to 95 percent of pollutants from the air, according to a NASA study. Enzymes in the leaves decompose formaldehyde, benzene, carbon monoxide and other substances into harmless ones. Like moss, the plant controls humidity.

Ivy

High filtering performance of up to 94 %
Including benzene and trichloroethylene, mold and mildew
As a climbing or ground-cover plant

Ivy is another very effective air filter. It fishes 94 % of pollutants from the air, according to the NASA study. As a house plant, ivy is particularly effective against mold and mildew. The plant is able to extract 80 percent of all mold and mildew spores from the room air within twelve hours.

Energy & decontamination

Multi-talent algae

Energy & decontamination: Multi-talent algae

Used to store energy
Basis for biofuels
Transformation of radioactive substances

Algae are a fascinating form of life. Like plants, they use photosynthesis to live, but achieve the conversion much faster which results in near-explosive growth. Algae can be used for biofuels, bioasphalt and as bioreactors for hot water and for heating buildings. At the same time, they serve to extract radionuclides such as radioactive silver, cesium, zinc, cobalt and uranium from the soil.

Decontamination

Microalgae reproduce by means of radioactive isotopes
Absorb and store radioactive particles
Can survive 4,000 times higher radiation dose than humans

In tests of a holding basin for spent nuclear fuel, single-celled microalgae fed on radioactive isotopes, so to speak. The result: The plant purifies the radioactive cooling water. To do so, it absorbs and stores radioactive particles. Thus, the algae survive an absorbed dose of 20,000 Gy. For comparison: A dose of five GY is enough to kill a human being. Scientists are planning to use the algae to clean up contaminated areas such as those in Fukushima and Chernobyl and make them habitable again.

Biofuel

Largely carbon-neutral fuels
Fast re-growth
Technologies not sufficiently investigated yet

Algae may be used as biofuel by means of various technologies. Some algae species can be used to produce oil, which can be transformed into a fuel comparable to diesel by means of ester interchange. Alternatively, the carbohydrates, which account for a large part of the algae mass, are transformed by fermentation into ethanol or, in gaseous form, into methane and carbon dioxide. The production of hydrogen is possible as well.

Bioreactor

Transformation of climate-killing CO₂ into energy
Requires only minimal space and care
Currently still in test stage

In special bioreactors, the single-celled organisms with a size of three to five micrometers reproduce very fast and are able to produce large amounts of energy in the form of biomass and heat. To do so, they merely require sunlight and CO₂. The heat is directly available for hot water and heating, while synthetic gas and subsequently methane can be produced from the algae biomass.