Eggshell Hydroxyapatite for Fluoride Removal

ISEF Category: Chemistry

Subcategory: Inorganic Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Your tap water can hide a problem you cannot see. Fluoride is helpful at low levels, but too much can become a health risk. You can turn kitchen waste, like eggshells, into a material that traps fluoride and measure how well it works. That makes this project part chemistry, part environmental problem-solving.

What Is It?

Hydroxyapatite is a calcium phosphate mineral. Your teeth and bones contain a similar material, which is why hydroxyapatite gets used in health products. In this project, you make a simple version from eggshells, which are rich in calcium carbonate. Then you convert that calcium source into hydroxyapatite and test whether it can remove fluoride from water.

Think of the material like a sponge with tiny binding sites. Fluoride ions stick to the surface or swap places with ions already in the solid. If you dope the hydroxyapatite with magnesium or strontium, you change the crystal structure a little. That can change how many fluoride ions the solid can hold and how fast it works.

Isotherm modeling helps you turn raw adsorption data into a real story. Instead of saying only that one sample worked better, you can ask which model fits best and what that says about the surface. That gives your project a stronger chemistry backbone.

Why This Is a Good Topic

This is a good science fair topic because you can change one variable at a time, like doping level or starting fluoride concentration, and measure a clear result. The project connects to drinking water safety, which gives it real-world meaning. You can also build skills in synthesis, calibration, adsorption tests, graphing, and model fitting, even if you are new to research.

Research Questions

• How does Mg²⁺ doping change the fluoride adsorption capacity of eggshell-templated hydroxyapatite?
• What is the effect of Sr²⁺ doping on the rate of fluoride uptake from water?
• Does the best-fit adsorption model change when the hydroxyapatite is doped with Mg²⁺ versus Sr²⁺?
• To what extent does pH affect fluoride removal by eggshell-derived hydroxyapatite?
• Which fluoride starting concentration gives the clearest separation between undoped, Mg-doped, and Sr-doped samples?
• How does particle size influence the fluoride uptake of eggshell-templated hydroxyapatite?

Basic Materials

• Clean eggshells.
• Calcium source and phosphate reagents for hydroxyapatite synthesis.
• Magnesium salt and strontium salt for doping trials.
• Distilled water.
• Fluoride test kit or fluoride ion selective electrode.
• Digital balance with 0.01 g or better resolution.
• Beakers, graduated cylinders, and stirring rods.
• Coffee filters or filter paper.
• pH strips or a pH meter.
• Drying tray or low-temperature drying oven.
• Notebook or lab data sheet.
• Safety goggles and gloves.

Advanced Materials

• X-ray diffraction instrument.
• Fourier transform infrared spectroscopy access.
• Scanning electron microscope access.
• BET surface area analyzer.
• Fluoride ion selective electrode with calibration standards.
• Orbital shaker.
• Centrifuge.
• ICP-OES or ICP-MS for solution verification.
• Analytical balance.
• Muffle furnace or controlled-temperature oven.

Software & Tools

• Google Sheets: Organizes adsorption data, calculates percent removal, and graphs isotherms.
• ImageJ: Measures particle size and compares surface texture from microscope images.
• R or Python: Fits Langmuir, Freundlich, or other adsorption models and compares error metrics.
• PubChem: Helps you check reagent identities, formulas, and safety data.
• NIH PubMed: Finds review articles and past adsorption studies to guide your methods.

Experiment Steps

1. Define the one material change you will test first, such as no dopant, Mg²⁺ doping, or Sr²⁺ doping.
2. Plan how you will confirm that your eggshell-derived solid really became hydroxyapatite before you test fluoride removal.
3. Choose the fluoride measurement method and build a calibration curve so your readings become usable numbers.
4. Design the adsorption comparison so each sample sees the same water chemistry, except for the variable you change.
5. Select the isotherm models you will fit, then decide which summary stats will tell you which model fits best.
6. Map out controls for background fluoride loss, container adsorption, and pH effects before you collect the main data.

Common Pitfalls

• Skipping material verification, which leaves you unsure whether you made hydroxyapatite or a mix of calcium salts.
• Using muddy or uneven eggshell powder, which creates batch-to-batch variation in adsorption results.
• Measuring fluoride with no calibration curve, which turns relative color changes into weak data.
• Ignoring pH control, which changes fluoride chemistry and can make one sample look better for the wrong reason.
• Comparing samples with different particle sizes or stirring conditions, which confounds doping effects with surface area effects.

What Makes This Competitive

A stronger project will not stop at a before-and-after fluoride test. It will compare dopants, fit more than one isotherm model, and explain why the best model fits the data. Strong entries also track controls carefully, especially pH, surface area, and blank losses. If you add characterization data, like XRD or SEM, your chemistry story gets much stronger.

Project Variations

• Test fluoride removal from synthetic water at different pH levels to see how acidity changes adsorption.
• Compare eggshell-derived hydroxyapatite with a commercial calcium phosphate material to benchmark performance.
• Study how Mg²⁺ and Sr²⁺ doping change adsorption when the fluoride source comes from real tap water samples.

Learn More

• PubMed: Search review articles on hydroxyapatite adsorption, fluoride removal, and calcium phosphate materials.
• NIH PubChem: Check chemical properties, formulas, and safety details for calcium, magnesium, strontium, and fluoride reagents.
• USGS Water-Quality Resources: Look for fluoride facts and drinking water context from the U.S. Geological Survey website.
• NOAA Water Resources Education: Find clear background on water chemistry and contaminant transport from NOAA educational pages.
• MIT OpenCourseWare: Search inorganic chemistry and materials chemistry lecture notes for crystal structure and adsorption basics.