The free icons have different licenses, so this question can't be answered by a yes or a no.
To use an icon for commercial purposes you will have to click the icon you want to use and read the license that applies for this icon. This information is found just below the icon. There is a clickable link to the license terms. If the icon cannot be used for commercial use, this will be clearly stated.
To make it easier for you to find icons you can use, we have made a filter at the top of the search results. With this license filter you can remove all icons that are only for personal purposes.
If you have any questions regarding licenses, please check our License Overview article.