Methods of pulp fiber treatment

A method of bleaching pulp, comprising a bleaching process including a bleaching sequence comprising:

• first contacting a pulp with a singlet oxygen source;
• after the first contacting, second contacting the pulp with an alkaline peroxide source;
• and
• after the second contacting, contacting the pulp with chlorine dioxide:
• wherein the singlet oxygen source comprises a peracetate oxidant solution comprising peracetate anions and a peracid, and wherein the peracetate oxidant solution as added to the pulp for the first contacting has a pH from about pH 10 to about pH 12 and a molar ratio of peracetate anions to peracid ranging from about 60:1 to about 6000:1;
• and
• wherein the bleaching sequence is in the absence of contacting the pulp with chlorine dioxide between and during the first contacting and the second contacting.

A method of bleaching pulp, comprising:

• first contacting a pulp with a singlet oxygen source;
• after the first contacting, second contacting the pulp with a chelating agent;
• after the second contacting, third contacting the pulp with an alkaline peroxide source;
• after the third contacting, fourth contacting the pulp with chlorine dioxide;
• and
• after the fourth contacting, fifth contacting the pulp with an alkaline peroxide source;
• and wherein:
• the singlet oxygen source comprises a peracetate oxidant solution comprising peracetate anions and a peracid, and wherein the peracetate oxidant solution as added to the pulp for the first contacting has a pH from about pH 10 to about pH 12 and a molar ratio of peracetate anions to peracid ranging from about 60:1 to about 6000:1;
• the peracetate oxidant solution comprises a molar ratio of peracetate to hydrogen peroxide of greater than 16:1, and
• the method is in the absence of contacting the pulp with chlorine dioxide between and during the first contacting, the second contacting and the third contacting.