Liao Xiang-ru and Wang Yi-chun, two third-year students at National Changhua Girls' Senior High School, have come up with a way to make use of chalk stubs that were too short to be used again. The girls ground down the stubs and then added the perfect amount of heated plaster and water, creating new pieces of chalk. The work by the two girls helped earn them first prize in the Toyota Environmental Protection Summit event that encourages students to make their school campuses greener. The project by the two girls was selected from over 1,600 submissions in a finale held Sept. 18 in Taichung.
Liao and Wang stated that students frequently see lots of chalk stubs in the classroom that are too short to be used anymore and are simply tossed into a box. They decided to use knowledge learned in their chemistry class on how heated plaster and water hardens when it cools, and apply this to chalk. With guidance from their chemistry teacher, Zhang Wen-ping, the two girls first ground up the remaining bits of chalk and mixed it together with heated plaster and water. After countless attempts over several months, the girls finally were able to find the correct ratio of the various components, enabling them to produce new pieces of chalk.
The two girls commented that the main ingredient of chalk is calcium carbonate or calcium sulfate. After grinding down the chalk into powder, they added water and heated plaster in a ratio of 10-to-5-to-1 or 10-to-9-to-4, which helped to create the best results. They then used newsprint that exhibited a high degree of absorption to create molds. They turned to the sun to dry the mixture naturally, instead of putting it in an oven. The result was stick after stick of chalk.
Liao and Wang remarked that while chalk is cheap, the ability to recycle the chalk bits will be able to save schools a considerable sum each year. At the same time, this helps schools to do their part in protecting the environment, they said.
Zhang, a chemistry teacher, said about two pieces of chalk are used in each class, which means that the school each day uses over 720 pieces of chalk. Zhang extrapolated this further to show that some 2.4 million pieces of chalk are used each day in Taiwan. Each box of chalk contains 80 pieces and sells for a price of NT$35 (US$1.17). Zhang added that figuring that class is held 200 days a year, recycling chalk could save the school system about NT$210 million annually.
Kong Jian-guo, principal of National Changhua Girls' Senior High School, said the school plans to promote the project of the two students, who will serve as seed instructors and go to other schools to show their peers how to recycle chalk.