df['ESTACD'].unique()

Output:
array([11.0, 32.0, 31.0, 35.0, 37.0, 84.0, 83.0, 81.0, 97.0, 39.0,
   38.0, 40.0, 34.0, 7.0, 17.0, 16.0, 14.0, 82.0, 8.0, '11', '40',
   '31', '39', '68', '97', '32', '33', '37', '38', '83', '84', '93',
   '35', '81', '67', '07', '80', '71', 'A3', '14', '17', '22', '34',
   '36', '82', '08'], dtype=object)

for i in range(len(df)):
    if (type(df['ESTACD'][i]) == float) or (df['ESTACD'][i].startswith('0')):
        df['ESTACD'][i] = str(int(df['ESTACD'][i]))