Ferric Citrate

It is a dark orangeish or reddish brown solid, slightly soluble in hot water yielding an orange or orange-yellow solution at pH < 2.0.[1][2] The solution becomes green at pH > 2.0.

Ferric citrates play important roles in the metabolism of iron by living organisms. Citrate anions are released by plant roots and some microorganisms in order to extract iron from insoluble compounds in the soil, such as ferric Hydroxide, and form soluble ferric citrates that can be absorbed by the organism.