Additionally you can always determine the column name from its position as dataTable.Columns(index).ColumnName.
However, I also thought of a different solution for your problem:
Clone the original datatable, e.g. dt2 = dt1.Clone, this gives you an empty table with the same column structure as dt1;
Set the Unique property to True on relevant columns (or all) to enforce uniqueness, e.g. For Each column in dt2.Columns, column.Unique = True;
Loop over the original table and add its rows to the clone with the Add Data Row activity: For Each row in dt1, Try Add Data Row, Catch ConstraintException. It is good practice to log any exception message, but you don’t need to do anything with it as it is just used to ignore the duplicates.