Is the expiation for an oath (kaffarat al-yameen) paid to a charity from money mixed with interest considered valid?

The expiation for an oath is feeding ten poor people or clothing them, or fasting three days for those who cannot afford the former. It is permissible to appoint another person to give it out on one's behalf.

It is forbidden to deposit money in savings and investment accounts in usurious banks. One must withdraw from them and dispose of the usurious interest by giving it to the poor or spending it on public welfare. It is permissible to deposit money in a current account for safekeeping when necessary.

It is not permissible to give the expiation from usurious interest if it can be distinguished from the principal amount. However, if the interest has commingled with the principal, then after disposing of the usurious interest, the remaining money becomes permissible, and it is allowed to give the expiation from it. If the expiation was given from money mixed with usury unknowingly, there is no blame, and the expiation is valid, but one is only required to dispose of the usurious interest.