The four sentences (labelled 1, 2, 3 and 4) given below, when properly sequenced, would yield a coherent paragraph. Decide on the proper sequencing of the order of the sentences and key in the sequence of the four numbers as your answer.

1. Veena Sahajwalla, a materials scientist at the University of New South Wales, believes there is a new way of solving this problem.

2. Her vision is for automated drones and robots to pick out components, put them into a small furnace and smelt them at specific temperatures to extract the metals one by one before they are sent off to manufacturers for reuse.

3. E-waste contains huge quantities of valuable metals, ceramics and plastics that could be salvaged and recycled, although currently not enough of it is.

4. She plans to build micro factories that can tease apart the tangle of materials in mobile phones, computers and other e-waste.

The correct sequencing of the sentences is 3142.

Let's analyze the sentences step-by-step to build a coherent paragraph:
1. Sentence 3 introduces the main topic, which is "E-waste" and the problem associated with it: "E-waste contains huge quantities of valuable metals, ceramics and plastics that could be salvaged and recycled, although currently not enough of it is." This sets up the context and identifies the problem of un-recycled e-waste.
2. Sentence 1 follows directly by introducing a person who has a solution to this problem: "Veena Sahajwalla, a materials scientist at the University of New South Wales, believes there is a new way of solving this problem." The phrase "this problem" in Sentence 1 refers back to the issue mentioned in Sentence 3 (that not enough e-waste is recycled). Therefore, 3-1 is a logical link.
3. Sentence 4 expands on how she plans to solve it: "She plans to build micro factories that can tease apart the tangle of materials in mobile phones, computers and other e-waste." The pronoun "She" refers to Veena Sahajwalla introduced in Sentence 1. Thus, Sentence 4 follows Sentence 1.
4. Sentence 2 describes the detailed execution of her plan in the micro factories: "Her vision is for automated drones and robots to pick out components, put them into a small furnace and smelt them at specific temperatures..." The possessive pronoun "Her vision" refers to the plans described in Sentence 4. Thus, Sentence 2 naturally concludes the paragraph by explaining how these micro factories will operate.
Therefore, the correct sequence is 3-1-4-2.