Lithium Iron Phosphate Batteries, page-5

The LiFePO4 battery take up will simply be a large additional source of demand for phosphoric acid and therefore good for sustained higher rock phosphate prices.

As Tcb007 says we aren't even looking at phosphoric acid production, simply phosphate rock sales as the capital cost for the infrastructure would probably erode the NPV compared to selling rock. The direct to farmers sales of DARP is, however, a genius way to eke out some more margins from the deposit with little to no extra upfront capital cost.