Meta query problem

I have this code:

'meta_query' => array(
	'relation' => 'AND',
 	           array(
		        'key' => 'n_de_personas',
		        'value' => $selection1,
		        'compare' => '='
                   ),

And it works fine getting from the database the posts whose value of the key matches the value of $selection1 variable. But I need it to work for the values that match $selection1 and bigger ones. So I modified the code to:

'meta_query' => array(
	'relation' => 'AND',
 	           array(
		        'key' => 'n_de_personas',
		        'value' => $selection1,
		        'compare' => '>='
                   ),

And it also works, but only from 0 to 9. When it compares over 10 it goes wrong. Please could anybody help?