Get avatar URLs only from an array of newest members

Hello everone, my question is how do I list only the avatar URLs  on a non-object array? Doing $newest_members->getIconURL('large') would white screen the page.

<?php
$newest_members = elgg_list_entities_from_metadata(array(
'metadata_names' => 'icontime',
'type' => 'user',
'limit' => 18,
'full_view' => false,
'pagination' => false,
//'list_type' => 'gallery',
//'gallery_class' => 'elgg-gallery-users',
'size' => 'medium',
));
echo $newest_members;
?>