Our process
Our Process is applicable on many ways
Our process can begin with many different sources. As platinum accumulate in many places, its recovery can begin from a lot of places and substrates. In fact the first step of our project would change if the basic matter change. Moreover, solutions of phytoremediation provide a lot of substrates and by-products our project could start from.
Indeed our process could start from ashes
The Source (step1)
Sewage Sludge
(Incineration)
Ashes
Bioleaching
The Bioleachning process allow a far better recovery of platinum. Indeed, the drop of pH is required for the metals )solubilization. This step is usually realized with chemicals as chlorhydric acid in the actual industry. But in order to achieve a greener process as possible, we decided to lower the pH with biological ways, as the leachning accomplished by Thiobacillus. This method is widely use in mines, e.g. for copper mines in South America, so this will be a reliable step already tested in industrial conditions.
This method rely on the ability of the bacteria Thiobacilus to acidify its medium until a pH of 1. The bacterium solution is applied on the ashes and liquid part dropping from it constitute the leachate i.e. a very acidified solutions containing solubilized metals particles mostly in ionic form.
This step wouldn't be obligatory in our process, but it could improve our recovery yield while still using a environmentally friendly approach.
Recovery
Once the platinum is leached, we need to recover it. If leaching (by biological or chemical methods) is clearly recommended to improves solubilization of metals, it does not improves the concentrations. As we worked with synthetic biology, we decided to use what it is commonly employed by cells to catch metals, i.e. siderophore. Siderophores are well known to catch iron most of all but some of them have an affinity with others metals as platinum. So in our process, we planned to work with such a siderophore, called Desferrioxamine B. This one is already employed to recover platinum in mines, and have shown high capacity to recover platinum from ores [1].
Recovery yields with DFHOB can reach 75% of the total platinum if both of these conditions are fully respected: a lowering pH level leaching step should be performed, as well as a alcanization of medium (until a pH range between 8 and 9) before addition of siderophore. The last step devoted to rise up the pH level will be realized using a standard buffer, e.g. a Tris buffer.
So where is the innovation in this step? Firstly, in our case, DFHOB won't be applied on the same materials where is commonly used, in our cases not ores but a leachate of ashes. Basically the main difference will be the metal concentration.
Secondly, DFHOB is usually synthesized chemically, we'll rather produce it in high amounts with bacteria. Indeed, operon of the Desferrioxamine B biosynthesis will be cloned into a E. coli bacteria strains in order to produce it, hence lowering the costs of required basic matter as production by bacteria needs especially an appropriate medium and good growth conditions.
DFHOB is a derivative of Diamines moelcule and therefore its Biosynthesis start with a amino acid, lysine. Lysine is quite expansive, and as we are aware about the cost of our process we decided to use a cheap source of lysine the corn steep liquor. Such a lysine source is already in use in industry since it's cheap, amino acid provided, produced in industrial amounts and well known as a excellent source of nitrogen in growth media.
- ↑ Bau and al., 2015 http://dx.doi.org.gate1.inist.fr/10.1016/j.hydromet.2015.01.002
Glossary
'DFHOB': Desferioxamine B, a molecule able to catch metals with a very high affinity, as platinum.
'Corn steep liquor': a by-product of an industrial process (wet-milling) applied on corn kernels. As the kernels are steeped in water solution, the process produce an amino acid, vitamins and minerals enriched solution in high volumes.
