Add-PSSnapin "Microsoft.SharePoint.PowerShell"

$webUrl = "http://acme.local/site/ss/"
$listtName = "Some List"

$w = get-spweb $webUrl
$l = $w.Lists.TryGetList($listtName)

$spQuery = New-Object Microsoft.SharePoint.SPQuery
$spQuery.ViewAttributes = "Scope='Recursive'";
$spQuery.RowLimit = 4900
$caml = "<Where><Neq><FieldRef Name='_ModerationStatus'/><Value Type='ModStat'>0</Value></Neq></Where>"
$spQuery.Query = $caml 

$ii = $l.GetItems($spQuery)

$ii | % {
	$i = $_
	if($i.ModerationInformation -ne $null){
		$i.ModerationInformation.Status = [Microsoft.SharePoint.SPModerationStatusType]::Approved
		$i.ModerationInformation.Comment = 'Automatically Approved'
		$i.Update()
	}
}