Is it permissible for me to keep what I acquired from my salary earned while working for a loan company?

The ruling concerning salary is based on the ruling concerning the work itself. If the work is permissible and unrelated to Riba (usury/interest), then there is no harm in benefiting from the salary. Otherwise, it is an illicit gain that must be disposed of by spending it on the welfare of Muslims or giving it to the poor and needy. It is not permissible to keep it unless the person is poor and in need, in which case he may take from it what suffices his need.