How to make homemade lead-free preserved egg?

Preserved egg, commonly known as alkali eggs, is one of our traditional flavor egg products. Preserved egg with parsley has been the most popular dish in our office girls! However, how to make preserved egg? After searching from Internet, I find the clear method that is even made by the help of zinc sulfate powder.
 
First, prepare liquid A: Pour water 50 liters each in two containers, one container add tea 2.5 kg, another vessel add fresh cypress leaves 2.5 kg. Boil the two for 1 hour, then put two the tank of liquid filter to a container filled with 3 kg salt. After salt melted, add 50 liters boiled water, and eventually add cold water up to 150L. Stir it well until cooling, then it’s named liquid A.
 
Second, prepare liquid B: Mix liquid A 90L with salt 2 kg and zinc sulfate 300g together in a container. Then add 96% sodium hydroxide 6 kg in to the container. When it has been cooled, add liquid A up to 100L, swirling. It’s liquid B.
 
Third, first dip: Dip the fresh duck eggs into liquid B, keep it under normal temperature for 13 days.
 
Fourth, repeat dip: Mix 50L liquid A that’s used to firstly dip with 50L liquid B. The mixture is repeat dip solution. Keep it under normal temperature for10 ~ 15 days and then pick the eggs out.
 
Finally, paraffin wax treatment: Dip the eggs above into paraffin liquid for 3 ~ 5 seconds. Till the eggs cooled, take them out. Now we get the products.
 
In this way, the preserved eggs not only don’t contain any lead. Dipped by zinc sulfate, the preserved eggs also contain zinc that’s more beneficial to human body, and preservation period is prolonged for half a year.