What is the ruling on greeting female colleagues who do not return the greeting and do not wish to speak, and should one greet them or not?

Initiating greetings (salam) is sunnah (recommended), while returning a greeting is fard kifayah (a collective obligation). Do not stop greeting them; instead, recall the Prophet Muhammad's (peace be upon him) saying: "You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I not tell you about something which, if you do it, you will love one another? Spread salam amongst yourselves." Spreading salam is one of the greatest causes of harmony and affection. It is also a discipline for the soul and an act of humility, and it removes discord and abandonment. Salam should be for Allah, not for whims. Continue to offer greetings with a sincere intention; perhaps Allah will unite hearts.