How to remove pink stains from white marble?

[rafael]

Hello, i'm a chemistry from a brazilian marble industry. I have many white dolomitic marble with pink stains, probably comes from a manganese-rich environment on the nature. The current treatment to removal consists on complexation with thioglycolate and bleaching with hydrogen peroxide, but it's not a satisfactory result. Sometimes it works, sometimes not. Do you know better treatments of these stains? Or know some literature about those pink stains? 

Thanks!