Sustainable Solutions

Bioleaching of Rare Earth Elements

Bioleaching of Rare Earth Elements (REE) from Mine Waste

Bioleaching is a sustainable method leveraging microbial activity for extracting Rare Earth Elements (REE) from mine waste. This process utilizes naturally occurring or genetically engineered microorganisms to solubilize metals from solid matrices, offering an eco-friendly alternative to traditional extraction methods.

Microorganisms such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans play pivotal roles in bioleaching. These bacteria oxidize sulfide minerals, generating sulfuric acid and ferric iron, which subsequently dissolve REE-containing minerals. The efficiency of bioleaching depends on various factors including pH, temperature, oxygen availability, and the presence of specific nutrients.

Carbon  Sequestration

Chemical production wastewater has the potential for CO2 capture due to its natural abundance of dissolved carbonates and bicarbonates, which act as buffers for CO2 sequestration. Introducing CO2 activates favorable reactions that convert these carbonates and bicarbonates into stable minerals like calcite (CaCO3) and magnesite (MgCO3), effectively capturing and storing the CO2. However, efficiency relies on saturation indices (SI). Positive SI for barite (BaSO4) or celestite (SrSO4) indicates scaling risks, while high SI for calcite and magnesite is desirable as it signifies a higher likelihood of capturing CO2. While calcite and magnesite precipitation are the goal for CO2 capture, excessive precipitation leads to scaling problems. High calcite SI can cause it to precipitate on equipment, hindering wastewater treatment. Similarly, high barite SI leads to scaling and equipment damage. Optimizing CO2 capture requires controlling operational parameters like pH (slightly acidic favors desired minerals), temperature (lower for calcite), and residence time to promote CO2 capture while minimizing scaling issues. While wastewater presents a potential for CO2 capture, several challenges need to be addressed. The specific composition of the wastewater significantly influences its CO2 capture potential and scaling tendencies. Depending on the specific effluent, pretreatment steps might be necessary to remove problematic components that could interfere with CO2 capture or promote unwanted scaling. Furthermore, ongoing research and pilot studies are crucial for optimizing CO2 capture processes for various types of chemical production wastewater. By overcoming these challenges, this technology has the potential to become a viable strategy for the chemical industry to contribute to CO2 emission reduction goals.

Geologic Hydrogen A Promising Natural Resource for the Future

Hydrogen has been considered as a key resource in the clean energy transition but producing it efficiently hasn't always been easy. Now, a new prospect is emerging from deep within the Earth: geologic hydrogen. This naturally occurring form of hydrogen holds huge promise as a sustainable and abundant energy source.

Geologic hydrogen isn’t a recent development. It's been forming underground for millions of years through various natural processes. One such process is serpentinization, where water reacts with specific rock types, releasing hydrogen. Another is the breakdown of water molecules by natural radioactivity (radiolysis). These processes have potentially created vast reservoirs of hydrogen trapped beneath the Earth's surface.

Enhanced rock weathering (ERW)

Enhanced rock weathering is a carbon removal strategy that speeds up the natural process of rock weathering to store atmospheric CO2 in rocks. It is one of several “carbon removal” techniques that target carbon dioxide (CO2), the most important climate-warming greenhouse gas humans have been adding to the atmosphere. It exploits the natural carbon cycle where rain weathers rocks, releasing minerals that react with CO2 to form stable minerals like limestone, thus reducing atmospheric CO2 levels. However, natural weathering is too slow to address human-induced climate change.

ERW methods include grinding rocks like olivine and basalt into fine particles to increase reactivity with CO2. Olivine could be spread on beaches or in oceans to lock up carbon, also aiding in reducing ocean acidification. Basalt has shown potential in agriculture, capturing carbon and enhancing crop growth.

Mineral trapping, a related technique, involves injecting CO2 dissolved in water into underground basalt, where it mineralizes rapidly. Despite its potential, ERW faces challenges: the energy-intensive processes of mining and grinding rocks, the need for large land areas, complex chemical reactions, and potential ecological impacts. The cost is a significant barrier, with ERW being more expensive than direct emission reduction strategies like renewable energy development. ERW requires further exploration and development to become a viable complement to emission reduction efforts in the fight against climate change.