The most obvious casualties would be purveyors of fossil fuels, minerals, agricultural produce and other primary materials, the demand for which would suffer.

the demand for which would suffer为非限制性定语从句，关系代词which指代先行词fossil fuels, minerals, agricultural produce and other primary materials，并在定语从句中作介词for的宾语，for介词短语作主语the demand的定语。

如果逗号后加and则为并列句，which就还原为人称代词them.

, and the demand for them would suffer.

因为没有并列连词，后面就不是并列分句，于是将人称代词them改为关系代词which，就成了非限制性定语从句了。

另外，网友对先行词和关系代词的概念不够清楚。被定语从句修饰的词或词项，叫做先行词。which为关系代词，在意义上指代先行词，并在从句中作成分。当关系代词作介词宾语，介词短语又是主语的定语，则关系代词就可能位于定语从句的第四个词的位置。