I think what you're looking for is the disable_with
option and using a button.
http://apidock.com/rails/ActionView/Helpers/FormTagHelper/submit_tag
http://apidock.com/rails/ActionView/Helpers/FormTagHelper/button_tag
The reason for html not working in a submit tags is that they're turned into HTML input tag with the type submit.
<%= submit_tag "<p>Hi</p>" %>
<input type="submit" value="<p>Hi</p>">
Rails 3 Submit Tag + html_safe
<%= button_tag t('submit'), class: "btn btn-primary", id: "email_submitbutton", data: { disable_with: "<i class='fa fa-circle-o-notch fa-spin'></i> Processing Order".html_safe } %>
Also, I highly suggesting using a Font-Awesome gem.
https://github.com/FortAwesome/font-awesome-sass
This is cool because it means you don't need to hand write HTML in you're Ruby code.