All Sugar is Kosher, it does not require certification.
Although sugar is filtered through carbon which is produced from charred animal bone, and it is this that gives sugar its brilliant white colour, it is still 100% Kosher, LeMeHadRin.
Here are the reasons why this is so. Firstly, the bones are significantly altered from their initial state, they are deemed to be, in the eyes of Halacha, a new item. Furthermore in their new state, they are unfit for human consumption. Finally, the bone-char is removed from the sugar, it is not evident in the final product.
Although anti-foaming agents used in sugar production, may be of non-kosher animal origin, the amount used is insignificant and if used, would be Battel, nullified in the sugar.
For Passover we need to be concerned about confectioner's sugar or powdered sugar. This sugar is crushed to a very fine powder, and often a free-flowing agent is added to prevent the sugar from clumping. Often, the free flowing agent is not Battel since it is more than the acceptable proportion of 1:60. If cornstarch is used, Ashkenasim who do not use Kitniyos during Pesach, may not use this sugar during Pesach.
If wheat starch is used to prevent clumping, the sugar would be Chamets and must be sold before Pesach with the Chamets.
There is a rumour circulating that sugar manufacturers will "rework" the confectioners sugar into the regular sugar. This means that surplus confectioner's sugar for example, will be added to a regular sugar production.
This is ridiculous; no manufacturer in a first world country, indeed no sugar manufacturer maintaining HACCP or ISO standards would or could do such a thing. They are not going to contaminate their product. Besides the amount of starch would be truly Battel, Halachically insignificant.
The Star-K nevertheless suggests that it is best to purchase sugar with reliable Passover certification.