Modifying the Above Expression to the requirement stated :
Dt_Amount.AsEnumerable.Where(Function(x)x(0).ToString.Equals("AUTHORIZED") andAlso (x(1).ToString.IsNumeric andAlso CDbl(x(1).ToString)>0)).CopyToDatatable
Check if the above expression works. Let us know what is the output.
For Handling errors related to Direct CopyToDatatable, check the Tutorial post from @ppr above.