Compositions for bleaching pulps and their use

1. A composition for use in bleaching of pulps, the composition comprising:

(a) one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides or mixtures thereof; and

(b) a talc pitch control additive and, optionally, one or more pitch control additives selected from zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin-decomposing enzymes, cationic polymers, aluminium sulphate, polyaluminium chloride, dispersing agents, and mixtures thereof,

wherein the composition is an aqueous slurry having a total solids content of 10 wt.-% to 75 wt.-% on the basis of the total weight of the slurry,

wherein the weight ratio of the particulate alkaline earth metal oxide or alkaline earth metal hydroxide compared to the talc pitch control additive ranges from 9:1 to 1:9, and

wherein the talc pitch control additive is selected from micronized talc, bimodal talc, and cationic talc.

2. The composition according to claim 1 , wherein the particulate alkaline earth metal is selected from magnesium, calcium, and mixtures thereof.

3. The composition according to claim 1 , wherein the content of the particulate alkaline earth metal oxide or alkaline earth metal hydroxide ranges from 10 wt.-% to 90 wt.-%, and the content of the pitch control additive ranges from 90 wt.-% to 10 wt.-%, each on the basis of the total solids content of the composition.

4. The composition according to claim 1 , further comprising at least one of the following additives: (a) dispersants; (b) fillers; (c) surfactants; (d) bleaching agents; (e) chelating agents; and (f) pH-buffering agents.

5. A method of bleaching a pulp, the method comprising providing a composition according to claim 1 and mixing said composition with the pulp in such an amount that the particulate alkaline earth metal oxide or alkaline earth metal hydroxide is present in the pulp in an amount ranging from 0.2 to 4 wt.-%, and that said pitch control additive is present in the pulp in an amount ranging from 0.2 to 4 wt.-%, each on the basis of the total solids content of the pulp.

6. The method according to claim 5 , further comprising the addition of one or more of hydrogen peroxide, water glass, and a complexing agent to said pulp.

7. The method according to claim 5 , wherein the composition is added to the pulp during the bleaching step, or during the grinding step, or between the grinding and the bleaching step.

8. The method according to claim 5 , wherein providing the composition comprises sub-steps of

(a) providing one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides or mixtures thereof;

(b) providing one or more pitch control additives; and

(c) adding the compositions obtained from sub-steps (a) and (b) separately to the said pulp.

9. The method according to claim 5 , wherein said method of bleaching a pulp is a method of bleaching a pulp for papermaking.