The word iron is very often pronounced incorrectly by non-native speakers. It appears that the correct pronunciation is not usually taught in school.
The widely used but incorrect pronunciation is closely related to that of ironic. You can hear the incorrect pronunciation of iron here. The phonetic spelling of ironic in British English is [aɪˈrɒnɪk], whereas in American English it is [aɪˈrɑːnɪk], listen here. In both British and American English, the sound [aɪ] for the first letter in ironic is followed by an [r]. However, it is a mistake to assume that the same should be true for iron. Instead, the correct pronunciation is [ˈaɪən] in British English, and [ˈaɪərn] in American English, listen here. The crucial difference is that for iron, the sound [aɪ] is not followed by an [r]. In fact, there is no [r] sound at all in the British pronunciation, whereas the [r] in the American pronunciation comes after the [ə]. The origin of the pronunciation of iron is sometimes argued to be related to the German word eisern (meaning: made of iron), which rhymes to some extent with the correct pronunciation of iron.
The incorrect pronunciation can be heard in reference to the chemical element iron, and in every-day terms such ironing (English for Bügeln), or Iron Man (sports or movies), as in this film trailer
Because the mistake is so common, the pronunciation of iron is often quite a good indicator for the overall English language skills of a non-native speaker (and his/her English teachers). The pronunciation of other chemical elements is discussed here.
Finally, let us consider the word environment. According to the dictionaries, the standard pronunciation is [ɪnˈvaɪrənmənt], listen here. However, after hearing native speakers use other pronunciations on several occasions, I consulted the Longman Pronunciation Dictionary, which offers several other (not widely used) pronunciations. Most notably, some people pronounce -iron- in environment using the American pronunciation of the word iron, so that the complete pronunciation becomes [ɪnˈvaɪərənmənt]. (The British version, [ˈaɪən], is apparently not used, so that there is always an [r] in environment.) Another variation is to drop the middle n ([ɪnˈvaɪrəmənt]).