The heavier cell membrane fragments are then removed though high speed centrifugation. The membrane fractions can then be disrupted with strong detergents and then fractionated while the soluble fraction can be fractionated directly. Proteins have differing solubilities in this salt. At best you might expect a 2-3 fold purification. This is the pH at which the protein has no net charge and hence will not stick to a charged matrix.
Columns can be both positively or negatively charge.
An anion exchanger is positively charged and exchanges anions. In this technique beads containing small channels within them are used. There are many grades of these for separating compounds of differing sizes. If the compound is small enough is will travel both around the beads and through the channels thus increasing the time it is on the column. For this reason larger compounds elute ahead of smaller ones.