Replace submit button with glyphicon in rails

Quick question. I have:

<%= f.submit "Like", class: "btn btn-large btn-primary" %>

and instead of the text reading "like" I would like to replace the whole button with the:

<span class="glyphicon glyphicon-thumb-up"></span>

symbol.

What would be the correct way in rails to replace the submit button with the thumbs up icon but have it do the same thing?

UPDATE

I found this:

<%= button_tag(type: 'submit', class: "btn btn-primary") do %>
  <span class="glyphicon glyphicon-thumbs-up"></span> 
<% end %>

But the only problem is that this still shows the button behind the glyphicon (even if I remove btn btn-primary). Does anyone know how to get rid of the button?

Thank you!