Aluminum and Bauxite Residue (BR)

Aluminum, a widely available metal, remained inaccessible until the development of the Bayer Process for concentrating aluminum oxide and the Héroult-Hall Process for electrolytic reduction of the oxide, innovations that emerged just before the last century. The extraction process generates a byproduct known as Bauxite Residue (BR), often referred to derogatorily as "Red Mud." To avoid the emotional weight of this term, I will use "Bauxite Residue" to emphasize its potential for valorization and transformation. For a deeper dive, refer to my earlier article on this topic.

As an inventor with a patent (US10749168B1) under my name, I aspire to develop batteries that can be constructed and maintained using simple "recipes" and readily available materials in developing regions. One of my experiments involved an Aluminum-Ion cell, which, despite not consistently recharging, led to the gradual formation of a substance resembling the aforementioned Red Mud. This article focuses on an intriguing result from my attempts to create an iron flow battery.

Iron Flow Batteries and Their Mechanics

Iron flow batteries typically utilize Iron Sulfate or Iron Chloride. Rust (Fe2O3 or Fe(OH)) is mixed with an acid to yield an iron salt in a liquid solution. Upon charging, part of the salt oxidizes to the Fe3+ state (~0.8v), while the remainder reduces, depositing metallic iron (Fe0) on the negative electrode at -0.44v. This process reverses during discharge, yielding approximately 1.24v. Although these batteries operate at a lower voltage, their economical materials allow for decades of cycling before capacity diminishes, making them ideal for grid storage applications.

Upon receiving my Bauxite Residue samples, I endeavored to construct a flow cell using just a few electrodes, some mud, and sulfuric acid. A colleague noted the challenges of converting BR with acid, as it requires substantial quantities for effective dissolution. This is because BR is comprised of around 60% iron oxide but also contains other metal oxides, residual NaOH, calcium, silicon, and various rare earth elements. Its basic nature demands further neutralization, yet its composition is not merely a blend of pure oxides; it consists of various rock structures and other components.

To see if I could dissolve the mud, I applied a significant quantity of sulfuric acid. While it worked to some extent, it was impractical for real-world applications—one ton of BR would necessitate over twenty tons of sulfuric acid, resulting in a hazardous mixture.

Minimal Processing: A Key Objective

While I believe it could still be used for grid storage, the initial approach was less than ideal. My colleague challenged me to create a battery that required minimal processing—essentially something that could be "scooped and charged."

Bauxite Residue as a Battery Intercalation Host

Modern batteries generally operate on the principle of intercalation. In a lithium cell, for instance, a crystalline structure of lithium iron phosphate is paired with graphite. Charging the cell strips lithium ions from the crystal, intercalating them between graphite layers. When using the device, these ions return to the iron phosphate crystal. John C. Goodenough received a Nobel Prize in Chemistry in 2019 for elucidating this mechanism.

I hypothesized that Bauxite Residue could serve as an effective cathode material due to its inherent capacity to hold aluminum, most of which had been extracted during its processing.

Unexpected Results: From Bauxite Residue to Clay

However, I encountered an unforeseen outcome. After mixing a 50:50 solution of BR and H2SO4, the mixture clumped, becoming unmanageable. Leaving it for several days led to a transformation; the clay shifted from a pale pink to a grey-pink hue, gaining a texture reminiscent of traditional clay. The mixture seemed to retain its shape and appeared smoother.

At this concentration, I expected the mixture to approach neutrality, as the basic BR should largely neutralize the sulfuric acid, yielding a pH around 7.

The Playful Scientific Method

With limited formal chemistry training, I often find myself making mistakes—sometimes even spectacular ones. To me, the process of invention and discovery resembles poetry. Engaging with batteries is calming, akin to sketching. I navigate through possibilities, considering alternative approaches to problems. Not all who wander are lost.

However, such exploration can impede progress. I meticulously record observations, hypothesize, and delve into research while experimenting. Sometimes I rediscover established principles; other times, I face humorous mishaps—like a lab filled with a cloud of rotten egg odor. I embrace the journey and take copious notes, sometimes methodically, sometimes whimsically.

Understanding Battery Components

A battery is composed of a cathode (+), an electrolyte on the cathode side (catholyte), a membrane or separator, additional electrolyte on the anode side, and an anode (-). The terminology in chemistry and physics varies based on which component transfers electrons. In batteries, we label the positive electrode as the cathode and the negative one as the anode, primarily because we describe the battery in its charged state. While I now suspect that BR serves as a cathode (+) material, I continued to explore its potential.

I experimented with the clay as various components of a cell and tested different anodes, including iron and aluminum, hoping to elicit galvanic behavior. However, the results showed only fleeting pseudocapacitance, leading me to realize that most of the material wasn’t actively participating in the cell. I could construct a similar battery at a lower cost without the mud, so I set the project aside for a while.

The Journey Continues: Discovering New Properties

While attending a conference in Greece, I listened to various scientists discuss their research. One speaker, John Anawati, touched on a topic related to a "neutral" clay-like substance derived from Bauxite Residue, which exhibited surprising hygroscopic properties. My clay resembled this, expanding in size due to moisture in the air.

Upon returning home, I found that an aluminum anode had nearly oxidized completely while sitting in a cell with a graphite cathode. The image accompanying this section illustrates the distinct layers of crystalline structures formed. Initially, both anodes looked like typical aluminum, but over time, a white crystalline layer developed, indicating ongoing oxidation. This was peculiar since aluminum typically passivates at neutral pH, creating a protective oxide layer. Yet, the oxidation appeared to penetrate beneath this layer, leading to continued deterioration.

Adding Water and Observing Reactions

I decided to introduce some water, suspecting acidity might be an issue. When I added an aluminum electrode, it passivated and the voltage decreased, confirming neutrality. Nonetheless, something in the clay seemed to affect the aluminum negatively. After a week of experimentation under mineral oil, the water changed dramatically, not just slightly. The clay shifted from pale pink to bone white, while the liquid took on a blue/purple hue.

Subsequent experiments yielded similar results, regardless of whether I used aluminum or just iron. Tiny bubbles formed within the clay over the months, and an unexpected whiff indicated the presence of hydrogen sulfide.

pH Testing and Surprising Acidity

Curiosity led me to test the pH of this unexpectedly acidic mixture. Strips turned maroon, indicating an acidic environment beyond measure. Investing in a pH meter confirmed my suspicions— the readings were too low for the device to capture. I sought to understand why this mixture was so acidic and what implications it had for the clay.

Spectrographic Analysis

When pH tests failed, I turned to spectrographic analysis. My makeshift spectrometer setup allowed me to generate an absorption spectrum, revealing peaks that suggested interactions with various ions. This led me to hypothesize that my mixture could facilitate hydrogen generation effectively.

Continuing to Experiment

In another experiment, I introduced hydrogen peroxide (H2O2), expecting to observe oxidation. Indeed, the solution exhibited distinct layers, further confirming the presence of various compounds interacting within the mix. I surmised that the blue fluid might be linked to silicon, titanium, or some unusual aluminum variant.

Ongoing Exploration

As I continue to investigate, I am eager to share my findings with the scientific community. This exploration might yield insights into the chemistry of Bauxite Residue and its applications. While the primary goal remains to create a functional battery, understanding the nature of this material is equally important.

Utility and Future Applications

The mixture’s ability to produce hydrogen during electrolysis raises questions about its potential for catalyzing hydrogen generation. Additionally, separating iron from Bauxite Residue could enhance the concentration of rare earth elements, presenting opportunities for various industries.

The clay appears to function as an anion exchange material that could have implications for numerous chemical processes.

Mechanism Hypothesis

I theorize that the clay structure may absorb O- ions from the water, releasing H+ ions into the solution, thereby forming a hydronium compound. This self-assembling structure may continuously extract iron and aluminum oxides, forming a unique backbone.

Replication Process

For those interested in replicating my experiments, here are the basic steps:

Step 1 — Create Anawati's Clay

In a heat-resistant container, combine 100 ml of H2SO4 with 100 g of Bauxite Residue, initially slowly, then progressively faster. Depending on the acid quality, up to 250 ml may be required to form a clay-like substance.

Step 2 — Dilution

Transfer the clay into two jars, adding around 250 ml of water. Cover both jars with mineral oil to exclude atmospheric moisture and keep them at room temperature.

Step 3 — Metals

In one jar, introduce aluminum to test for residual H2SO4; in the other, add metallic iron. Monitor the reactions and observe the results over time.

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