loop not working

hi,
I am using arguments to display multiple excerpts on my page but when i add post_mime_type. it doesn’t work.what is working also stops i.e the title etc.

$args=array(
  'orderby' =>'parent',
  'order' =>'asc',
  'post_type' =>'page',
  'post_mime_type' => 'image',
  'post_type' => 'attachment',
  'post__in' => array(8,14,17,19,21,23,25,27),

   );
   $page_query = new WP_Query($args);

while ($page_query->have_posts()) : $page_query->the_post();
   <div class="blocks">
   		<div class="imgHolder">
   			<?php //the_id();
				wp_get_attachment_url($attachment->ID, 'thumbnail', false, false)