Redirect from old site on WordPress to Codeigniter. Domain remain same

Solution:

Redirect OR RedirectMatch directive from mod_alias cannot match query string. You must use mod_rewrite like this:

RewriteEngine On

RewriteCond %{QUERY_STRING} wpsc-product=подвеска-сова-медь-duplicate [NC]
RewriteRule ^/?$ http://domain.com/?page_id=851 [L,R=301,B]

Make sure to keep this rules on top of your .htaccess.

Reference: Apache mod_rewrite Introduction