"用硫磺处理" can be translated as "treat with sulfur" or "sulphur treatment" (using the British spelling "sulphur"; the American spelling is "sulfur").
For example:
This material needs to be treated with sulfur to prevent decay.(这种材料需要用硫磺处理以防腐烂。)
The fruit undergoes sulphur treatment to extend its shelf life.(这种水果经过硫磺处理以延长保质期。)