Powershell memory usage in runspacepool - powershell

Question

i have a problem with code:
Measure-Command{ $controller=Get-ADDomainController -Filter *| Select -ExpandProperty Hostname
$users=Get-ADUser -Filter * |select samaccountname
$scriptblock={
param($samacc,$controller)
$result=#()
foreach($cont in $controller){
$RESULT=$result + (Get-ADUser -Server $cont -Identity $samacc -Properties lastlogon,whenchanged,displayname,title,company | sort-object lastLogon -descending | select-object enabled,displayname,samaccountname,title,company, #{Name="lastLogon";Expression={[datetime]::FromFileTime($_.'lastLogon')}},whenchanged)
}
$result|Sort-Object -Descending -Property LastLogon|select -First 1
}
$MaxThreads = 5
$RunspacePool = [runspacefactory]::CreateRunspacePool(1, $MaxThreads)
$RunspacePool.ApartmentState = "MTA"
$job=#()
$RunspacePool.open()
foreach($user in $users){
$PowerShell = [powershell]::Create().AddScript($scriptblock).AddArgument($user.samaccountname).AddArgument($controller)
$PowerShell.RunspacePool = $RunspacePool
$job+=[PSCustomObject]#{
Id = $_
Pipe = $PowerShell
Handle = $PowerShell.BeginInvoke()
Object = $Object
}
}
while ($job.Handle -ne $null){
$Completed = $job | Where-Object { $_.Handle.IsCompleted -eq $true }
foreach ($Runspace in $Completed){
$data=$Runspace.Pipe.EndInvoke($Runspace.Handle)
$data|Export-Csv d:\fulllist.csv -Append -Delimiter ';' -Encoding UTF8 -NoTypeInformation
$Runspace.Handle = $null
}
Start-Sleep -Milliseconds 100
}
$PowerShell.Dispose()
$RunspacePool.Dispose()
Remove-Variable controller,users,scriptblock,job,Completed,data,Runspace,RunspacePool,PowerShell
[System.GC]::Collect()
}
I create for each user instance with powershell command, and throw it to runspacepool. But i have about 35000 users and when i reach about 18000 for me start problem with connection\session. And to result table get only data for 22000 users. Powershell then dont free memory. How can i correctly manage close instances to free memory (for users that already write to file).May be i use wrong place for commands or wrong commands.