Iron Beats Aluminum in the Race to Strip Textile Dyes from Wastewater

Textile dyeing is one of the most water-hungry and polluting industries on the planet. Every kilogram of finished fabric demands roughly 125 to 150 liters of water, and a substantial share of the synthetic dyes used in the process—by some estimates between 20 and 50 percent—ends up discharged untreated into rivers and streams. More than 700,000 tons of dyes are consumed worldwide each year, and many of these molecules are built from complex aromatic structures that microbes simply cannot digest. One such dye, neutral red, is used to color cotton fibers and resists biodegradation, persisting in aquatic environments where it can inhibit photosynthesis, poison microorganisms, and even pose carcinogenic risks. Against this backdrop, a team of researchers at the University of Ngaoundere in Cameroon has delivered a rigorous head-to-head comparison of two electrode materials—iron and aluminum—in an electrochemical water-cleaning technique that is rapidly gaining attention as a sustainable alternative to conventional treatment.

The technique, known as electrocoagulation, sounds almost deceptively simple. Two metal rods are immersed in the contaminated water and connected to a direct current power supply. As current flows, the anode dissolves, releasing metal ions—in this case ferrous and ferric ions from iron, or trivalent aluminum ions—directly into the solution. Meanwhile, at the cathode, water molecules are reduced, generating hydrogen gas bubbles and hydroxide ions. The metal ions and hydroxide ions then combine to form a cascade of hydroxide and polyhydroxide species, ultimately precipitating as freshly formed, amorphous flocs of iron or aluminum hydroxide. These gelatinous particles act as molecular sponges, adsorbing dissolved and colloidal pollutants and sweeping them out of the water either by settling to the bottom or by floating to the surface on the rising gas bubbles—a process called electroflotation. Crucially, the coagulant is generated in situ, eliminating the need for added chemical reagents and slashing the volume of secondary sludge that plagues conventional coagulation-flocculation treatments.

In the new study, published in Discover Chemistry, the researchers treated 400-milliliter batches of simulated dye wastewater in a 500-milliliter glass reactor fitted with two rod electrodes spaced 1.5 centimeters apart—a configuration chosen to limit ohmic losses while preventing clogging. Sodium chloride was added as a supporting electrolyte to boost conductivity, and the team applied a voltage of 30 volts at currents ranging from 100 to 400 milliamperes. Dye concentrations were tracked by UV-visible spectrophotometry at 528 nanometers, the wavelength of maximum absorbance for neutral red, with removal efficiency calculated from the change in concentration using the Beer-Lambert law. All experiments were conducted at a controlled 25 degrees Celsius, and samples were withdrawn every ten minutes, filtered, and analyzed after a 30-minute settling period.

The first variable probed was current intensity, and the results revealed a striking optimum. With iron electrodes, dye removal climbed from 58.27 percent at 100 milliamperes to a peak of 92.12 percent at 200 milliamperes, then fell back to 90.94 percent at 300 milliamperes and 79.23 percent at 400 milliamperes after 60 minutes of electrolysis. Aluminum electrodes followed the same pattern but with higher values: 59.31, 98.58, 90.27, and 80.45 percent at the same four currents. The researchers attribute the initial improvement to the greater flux of dissolving metal ions and hydroxide flocs as current rises, while the decline at higher currents reflects energy wasted in parasitic side reactions—including the oxidation of chloride to chlorine species at the anode and excessive water oxidation—which consume electricity without contributing to dye capture. Aluminum’s superior electrical conductivity helps explain its edge at equivalent currents.

Initial dye concentration told a complementary story. At low loadings of 25 milligrams per liter, both systems excelled, with iron achieving 96.76 percent removal and aluminum 98.27 percent after an hour. As concentrations rose to 75 and 100 milligrams per liter, performance dropped markedly—iron managed only 80.32 and 61.65 percent respectively at 60 minutes. The explanation lies in stoichiometry: at high pollutant loads, the electrochemically generated coagulant becomes insufficient, and the dense accumulation of hydroxide ions and gas at the cathode can even create a physical barrier between the multiplying particles and the electrodes, choking off the process. pH, meanwhile, acted as a chemical switch that favored one metal over the other. Iron performed best under acidic conditions, removing 94.13 percent of the dye at pH 3, where ferric hydroxide complexes form most abundantly, while removal sagged to 56.46 percent at pH 11. Aluminum showed the mirror-image behavior, peaking at 96.24 percent under strongly alkaline conditions at pH 11, where polymeric hydroxy complexes polymerize most effectively, and dipping to 67.76 percent at pH 3.

The two metals also produced visibly different treatment dynamics. With aluminum electrodes, the effluent remained clear and stable, and the hydrogen bubbles rising from the cathode efficiently floated the flocs to the surface for removal. With iron, the water first turned yellow, then greenish and turbid, as iron(II) and iron(III) hydroxides formed, and floc removal proceeded mainly by settling rather than flotation. The team notes that for the same quantity of electricity, roughly three times more iron dissolves than aluminum, generating a correspondingly larger mass of flocs—a factor that shapes both the kinetics and the sludge-handling profile of each system.

To move beyond one-variable-at-a-time testing, the researchers employed response surface methodology coupled with a centered composite design, an statistical framework that maps how multiple factors interact simultaneously while minimizing the number of experiments required. Eighteen trials explored three variables—initial dye concentration from 25 to 100 milligrams per liter, pH from 5 to 9, and electrolysis time from 20 to 60 minutes—and the resulting data were fitted to second-degree polynomial models. Analysis of variance confirmed the models’ significance, with Fisher statistics of 8.86 for iron and 9.19 for aluminum and p-values of 0.008 and 0.0024 respectively. The coefficients of determination reached 90.88 percent for the iron system and 91.18 percent for aluminum, with adjusted values above 80 percent, indicating the models retain genuine predictive power without overfitting. A paired t-test found no significant difference between experimental and predicted efficiencies, and validation metrics—bias factors of 0.99 and 1.001 and accuracy factors of 1.007 and 1.003—fell comfortably within accepted thresholds.

The three-dimensional response surfaces uncovered subtle interactions that single-factor experiments would have missed. For iron electrodes, a strong synergy emerged between pH and electrolysis time: neither parameter could compensate for an unfavorable value of the other, and yields above 90 percent required combining alkaline pH with sufficiently long treatment. For aluminum, the surfaces displayed a dome-like morphology with a narrow optimal window centered near neutral pH and intermediate concentrations, reflecting the amphoteric nature of aluminum hydroxide, which dissolves as soluble species at both very acidic and very alkaline extremes. Optimization converged on remarkably similar conditions for both metals—around 62 milligrams per liter of dye—but diverged in the details. Iron reached its maximum predicted efficiency of 98.05 percent at pH 8.42 after just 25.68 minutes, while aluminum required pH 7.50 and 34.50 minutes to achieve 95.39 percent.

Experimental runs under those optimal conditions validated the predictions, delivering 97.54 percent removal with iron and 96.89 percent with aluminum. The iron system’s roughly ten-minute kinetic advantage translates directly into lower energy consumption per batch, an economically meaningful margin at industrial scale, and the authors recommend iron as the preferred electrode for treating textile wastewater. Both systems comfortably exceeded 95 percent efficiency, underscoring electrocoagulation’s credentials as a compact, easily automated, low-sludge alternative to biological treatment, chemical coagulation, and costly advanced oxidation processes. The team points toward future work on energy optimization, electrode reuse, and the recovery of the metal-rich sludge, but the central message is already clear: with the right electrode and a statistically tuned recipe, electricity alone can strip a stubborn synthetic dye from water in under half an hour.

Subject of Research: Comparative electrocoagulation removal of neutral red dye using iron and aluminum electrodes optimized by response surface methodology

Article Title: Comparative study of the use of iron and aluminum electrodes for the removal of neutral red by electrocoagulation

Article References: Richard, D., Blaise, K., Bong, A. M., Carelle, M. W. L., Danièle, B. K., Amos, K., & Samomssa, I. (2026). Comparative study of the use of iron and aluminum electrodes for the removal of neutral red by electrocoagulation. Discover Chemistry, 3(1), Article 553. https://doi.org/10.1007/s44371-026-00990-1

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00990-1

Keywords: electrocoagulation, neutral red, iron electrodes, aluminum electrodes, textile wastewater, dye removal, response surface methodology, central composite design, water treatment, electrochemistry, decolorization, optimization