Screen readers have adapted an now read CSS generated content. The comments on your question offer good feedback (even being from 2013 and with a few updates to JAWS since then). Note, if you are using a third-party icon font then you have no control whether or not those icons live in Unicode's Private Use Area.
Font Awesome uses the same technique as in your example and has caught some flack for just the issue you cite. As a result, Font Awesome came up with an accessibility page that may be of use to you.
If your icon is genuinely used only for decoration, and not to convey information, then this chunk of code from the FA accessibility page may work for you:
Icons used for pure decoration or visual styling
If you're using an icon to add some extra decoration or branding, it does not need to be announced to users as they are navigating your site or app aurally. Additionally, if you're using an icon to visually re-emphasize or add styling to content already present in your HTML, it does not need to be repeated to an assistive technology-using user. You can make sure this is not read by adding the aria-hidden="true"
to your Font Awesome markup.
<i class="fa fa-fighter-jet" aria-hidden="true"></i>
an icon being used as pure decoration
<h1 class="logo">
<i class="fa fa-pied-piper" aria-hidden="true"></i>
Pied Piper, A Middle-Out Compression Solution Making Data Storage Problems Smaller
</h1>
an icon being used as a logo
<a href="https://github.com/FortAwesome/Font-Awesome"><i class="fa fa-github" aria-hidden="true"></i> View this project's code on Github</a>
an icon being used in front of link text
As always, test with real users and make sure the absence of the icon does not harm meaning of the page (hide it from sighted users in testing and see if its absence is confusing to them).