Bone As Heavy Metal Filter  
   
     
   
     
  Experiment Plan  
   
     
 

Experiment Goals
To determine if bone will retain heavy metals as they pass through it.

 

Apparatus

There are two different types of bone to pass solutions through (image attached):

Fig.1 The first is a sample of porous bone – a solution will pass very quickly through it.

Fig. 2 The second is a sample of compact bone, which will be sealed at the end of a plastic pipe using silicone.  It will then be capped to prevent evaporation.  The water should pass through this sample slowly.

Stages

  1. Create two metal (zinc) solutions of a calculated concentration.
  2. Pass a solution through the each bone sample, and document the time it takes for the water to pass through it.
  3. Gather the solutions
  4. Calculate the concentration of metals which remain.
  5. Compare the concentrations - ‘before and after’ for each bone type.

For the initial test it would be ideal to use zinc as it has been proven to react with bonemeal very well. 

 
 

 

 

 
  Experiment Procedure - Test 1  
   
     
   
     
 

Initially a 100cm^3 test solution was created which contained 54% zinc sulphate (54g per 100cm^3).

The solution had a cloudy consistency. To ensure the solution was not over saturated, 2 further test samples were created.  The first contained 54g of zinc sulphate dissolved in 200cm^3 of water (27%) and the second contained 5.4g zinc sulphate within 100cm^3 of water (5.4%).  Even the very dilute concentrations of zinc were cloudy. This proved that the original sample was not over saturated.  When the crystals dissolved some particles are left suspended in the liquid.

 
     
   
     
   
     
  Proceedure  
     
 

1. The 500cm^3 test solution was created, containing 54% zinc sulphate.

2. The solution was mixed using a magnetic stirrer for around 30 seconds to ensure consistency.

3. 100cm^3 of the solution was passed through the both samples of bone, and the timer was started.

4. The solutions were gathered, after they had passed through the bone samples, and were then stored for analysis at a later date.

Time: 

The solution passed through the porous sample in around 8 minutes.  Around 15% of the solution was retained within the bone.

The solution passed through the compact bone sample in around 55 minutes.  A negligible amount was retained in the bone.

Potential Error

* It should be noted that most of the solution was observed exiting the compact bone via the sides of the sample.  This may be due to lower density at the sides of the sample or could suggest that the seal around the pipe was breached.

 

 
     
  Analysis  
   
     
  The two samples where analysed using an EDTA Titration.  
     
   
     
  pH Test  
     
 

Initially a pH test was conducted on the solutions. This was performed with an electronic pH meter, which was initially configured using two solutions, of set pH. The results are as follows:

Stock solution: 5.74

Porous bone: 5.66

Compact bone: 5.67

 
 

 

 
  EDTA Titration  
     
   
     
  For the Titration to work the solutions were diluted to the following concentration: 10cm^3  - 1000cm^3 (10/1000)  
     
 

20 cm^3 of each dilution was titrated against 0.01m EDTA.  This was performed by adding 1cm^3 ammonia buffer + 5 drops eriochrome black indicator .  The EDTA solution is added until the sample changes from pink to blue. This was repeated 3 times for each sample and the average was taken.  The results are as follows: (cm^3)
  
Stock solution = 30.2

Wmhole bone average =  30.7

Tube bone average = 30

 
     
   
 

 

 
     
  New Seal & Bone China  
   
     
   
     
 

Due to the broken seal on the original experiement, a second tube bone was created. The silicone based sealant was subsituted for an epoxy resin. For accuracy, a different section of bone was used. 75cm^3 of 20% zinc sulphate solution was poured into the tube. However, due to the compactness of the bone, it took three weeks for 5cm^3 of solution to pass through. This was not enough to perform a titration.

A section of unfired bone china clay was also tested, however none of the solutoin was able to pass through.

 
     
  Second Experiement  
   
     
 

Due to the time required for the solution to pass directly through the bone, a new experiement was devised to see if bone will absorb heavy metals.

This time, the samples of bone were left to soak in a 20% zinc sulphate solution. Each sample was subjected to different conditions, before being analysed to determine if any changes had taken place.

 
     
   
     
 

Proceedure

The samples of bone were divided into 3 groups of similar weights and placed in a beaker containing 200cm^3 of 20% Zinc Sulphate solution. The first was to be left to soak overnight at room temperature, the second was heated for a day and the third was left to soak for three weeks. The weight of the bones before the experiement were as follows:

Short Soak = 39.7g

Heated Soak = 39.6g

Long Soak = 39.9g

 

 
   
 

 

Ph Analysis

After the procedure the pH of each sample was taken. The results:

20% zinc sulphate stock solution = 5.80

Short Soak = 5.80

Heated Soak = 5.02

Long Soak = 5.57

 

Volume Change

The volume of the solution after the proceedure:

Short Soak = 186 cm^3

Heated Soak = 174 cm^3

Long Soak = 184 cm^3

 

EDTA Titration

10cm^3 of each solution was placed in a flask and diluted by 1000 parts (10/1000cm^3)

25cm^3 of the diluted solution was then titrated against 0.01 EDTA, using 2cm^3 of ammonia buffer and 5 drops of eriochrome black indicator. This was repeated 3 times and the average was taken:

Stock solution = 17.3 cm^3

Short Soak = 17.2 cm^3

Heated Soak = 18.4 cm^3

Long Soak = 16.4 cm^3

 

Weight

After the experiement the bones were left to drain for three weeks, before their weight was taken:

Short Soak = 41.7g

Heated Soak = 41.5g

Long Soak = 43.3g

 

 
     
  Results  
   
 

The calculations on the results were kindly performed by Dr. Linda Morris:

Each bone was soaked in 200mL of the 20% zinc solution. This is equivalent to adding 10.46g Zn to each.

Short soak bone
Absorbed 1.44 g Zinc in total which works out at 0.036 gram zinc per gram of bone

Heated bone
Absorbed 0.85 g Zinc in total which works out at 0.02g zinc per gram of bone

Long soak bone
Absorbed 1.9 g Zinc in total which works out at 0.048 g zinc per gram of bone.

From this it would seem that the amount of zinc absorbed is a function of time. The extra increase in bone weights apart from the calculated amount of zinc absorbed is probably due to their absorption of some sulphate from the solution as well.

 
     
  This short experiement shows that bone in its whole form will absorb zinc, in a similar manner to ground bone. This relates to other experiemental work which is being carried out on ground bone.  
     
 

Copyright Andrew Ross 2008