IRA contributions are limited; you cannot "dump the excess into a retirement account like an IRA" if the excess is more than $5500. Furthermore, as @firefly points out, you need to have earned income (technical term is compensation and it includes self-employment income, not just wages) to contribute to an IRA, and the limit mentioned above is actually the lesser of your earned income and $5500.
(There are other limitations for people with high gross income, but these likely will not affect you)
On the positive side, if your earned income is small, you can contribute your entire taxable earned income
including the money withheld by your employer for Social Security and Medicare tax and Federal, State and local income taxes to an IRA, not just your
take-home pay. For example, if your earned income is $5500 and take-home
pay after tax withholding is $5000, you are still entitled to contribute
$5500. So, where do you get that withheld money from so that it can be
put into your IRA? Well, it can come from the student loan or interest earned
from a bank or from the
dividends and capital gains on your investments, etc. Money is fungible;
it is not the case that only the cash received (or deposited into
your bank account) as your take-home pay can be contributed. Subject to
other limitations mentioned, your earned income can be contributed, not
just your take-home pay.