Extracting Unique data from two columns

Try this, I'm not sure how long it will take with 70,000 rows to check.

Option Explicit

Sub getUniques()
    Dim rColA  As Range
    Dim rColB  As Range
    Dim cl     As Range
    Dim str    As String

    Set rColA = Range(Cells(1, 1), Cells(Rows.Count, 1).End(xlUp))
    Set rColB = Range(Cells(1, 2), Cells(Rows.Count, 2).End(xlUp))
    For Each cl In rColA
        str = cl.Value
        If Application.WorksheetFunction.CountIf(rColB, str) = 0 Then Cells(Rows.Count, 3).End(xlUp).Offset(1, 0) = str
    Next cl
End Sub