Is there any riba involved in selling pure gold for mixed gold?
Question

                Is it permissible for me to exchange a diamond ring for gold directly with the trader? Please note that the ring is made of white gold set with a diamond. If that is not permissible, I hope that you can explain the correct way to exchange this ring for gold.
Praise be to Allah.
    It is not permissible to sell gold for gold unless two 
    conditions are met: the exchange should take place in the same meeting in 
    which the agreement was reached, i.e., hand to hand; and they should be 
    equal in weight, because of the report narrated by Abu Sa‘eed al-Khudri (may 
    Allah be pleased with him) who said: “Gold for gold, silver for silver, like 
    for like, hand to hand. Whoever gives more or asks for more has engaged in 
    riba, and the taker and the giver are the same.” Narrated by Muslim, 2971. 

    So it is not permissible to sell gold for gold of different 
    amounts or deferred payment; no differentiation is made between white gold 
    or other kinds of gold, because what is meant by white gold is nothing more 
    than gold to which some platinum has been added to make it white. In fact it 
    is still gold, but it is mixed with something else that did not change it 
    from being gold. This has been explained previously in the answer to 
    question no. 68039 

    An-Nawawi (may Allah have mercy on him) said concerning the 
    words of the Prophet (blessings and peace of Allah be upon him), “Do not 
    sell gold for gold or silver for silver unless it is same for same”: 

    The scholars said: This includes all kinds of gold and 
    silver, both high and low quality, sound and broken, jewellery and ingots, 
    and so on, whether it is pure or mixed with something else. There is 
    scholarly consensus on all of that. 
End quote from Sharh 
    Muslim. 

    Secondly: 

    The correct way to do this transaction is to sell the ring 
    for cash, then buy whatever you want of gold and other things with the 
    cash. 

    And Allah knows best.